Human Demodex-a sebaceous worm

Transcription

1 30 Human Demodex-a sebaceous worm Walai-orn Pratchyapruit Niramol Vashrangsi Institute of Dermatology Introduction As we have already known that human skin surface occupied by various commensals which provide the eco-micrological balance for healthy skin. Demodex mites are one of the most common permanent ectoparasites of the mammalian pilosebaceous unit. Under normal circumstances, they are harmless to their hosts and appear to be of no medical significance. However, it is noticed that the number of primary demodex infestation (demodicidosis*) at the Institute of Dermatology, BKK has increased during the past three years. Since the mites live on sebaceous glands, the author would like to lay the background of sebaceous gland function first before going through the mitesû role in normal and pathological skin conditions. Recent advance of laboratory technique help us to better understand several aspects of the sebaceous glandûs biology by which we would apply in dermatological practice. This holocrine gland, as it releases sebum by rupture of its cells, has three phases of physiologic function; 1) sebum production, 2) sebum stocking in the follicular reservoir, 3) excretion. After being secreted, the sebum accumulates in the suprainfundibulum of the hair follicle forming a reservoir then it is further excreted onto the skin surface. Originally, it is composed of glycerides and free fatty acids (57.5%), wax esters (26%), squalene (12%), and sterols (free and esters-4.5%). 1 Once secreted, oxygen and micro-organisms transform çnativeé sebum into certain components of the complex mixture of molecules which are clearly cytotoxic or irritant. The demodex *In here the authors use the terms of çdemodicidosisé refer to demodex infestation. This skin condition can be found under the terms of çdemodectic diseaseé çdemodectic mangeé or çdemodicosis (ses)é in several standard textbooks in dermatology.

2 31 mites derive their nutritive requirements from cellular proteins obtained by epithelial destruction. The lipolytic activity of the demodex lipase might cause or aggravate the pathological skin conditions through the hydrolysis of the triglycerides in sebum resulting the release of irritant fatty acids. 2-4 Demodex mite as a normal habitant Two species of demodex mites : Demodex folliculorum (DF) and Demodex brevis (DB) have been identified in humans. They usually present on the face including the forehead, cheeks, nose, eyelashes of the upper & lower eyelids, Meibomian glands, and epidermis/sebaceous gland/hair follicle of the scalp, in the external ear 5 and the nipples. 6-8 They have also been discovered on the penis, mons veneris, buttocks and in ectopic sebaceous glands in the buccal mucosa. Mites have been isolated from individuals of all ages, except neonates. 5 They are almost ubiquitous on adult skin but are infrequent in young children. 9,10 The demodex mite was prevalent about 26-29% of autopsy cases. 11,12 They can stay alive on dead bodies for a long time. The longest postmortem interval in the positive cases was about 55 hours. Somebodies were infested by single species and the other being infested by both i.e. DF -51%, DB -2% and the two of them -19%. 13 A rise of the mite number is demonstrated in advancing age, either healthy individuals or autopsy cases, i.e. 4% in the young, 30% in the age group between years, and 47% in the elderly It is likely that with adequate sampling techniques, mite could be discovered in some folliculitis in the entire adult population. 5 The relationship of the mite number and host gender, skin type, hygiene, use of cosmetics, sun/other UV light exposure is still controversial. 15 However, one report found that males tended to be more heavily infested than females, in particular for DB. 16 Pregnancy shows no increase prevalence of mite density. 17 Regarding to the distribution of the DF and DB on the body, it seems that DF is more predominant than DB, but the latter has a wider distribution than the first and is more commonly found on the trunk. The ecologic and epidemiologic difference between the two species really exists and their roles on a variety of disease states should be distinguished in future study. 16 Demodex mite as a pathogen Demodex mites affect only a small number of people and only few cases of demodicidosis have been reported in children aged below 5 years. Most of the young patients suffered from leukemia or HIV infection. 9,10 The mites are discovered on several existing skin conditions. For example; facial itching with/without erythema, acneiform eruption without telengiectasia or flushing, blepharitis, seborrheic dermatitis, papulopustular eruption on the face or scalp, rosacea-like demodicidosis, acne rosacea, perioral dermatitis, and skin lesions of immuno-suppressed patients who on chemotherapy or with acquired immunodeficiency syndrome (AIDS). 17,18 In an exceptional case, the mites is reported to cause pathological lesion in the oral cavity. 19 How-

3 32 ever, there is no certain at what degree the mites are causative of and how they might contribute to the skin pathology. Based on clinical symptoms together with positive acarological findings, the demodicidosis can be classified into primary and secondary types. The first represents the skin lesion caused by the mites as an etiologic organism, the latter represents the existing skin diseases coexists with high prevalence of the mites. Thus, the diagnoses of demodex blepharitis, demodex folliculitis, demodex abscess, demodectic alopecia should be considered as primary demodicidosis because they are cleared up after eradication of the mites. 20 Immune response to demodex mites Although the demodex mites are found inoffensive on human skin, this relationship is putatively derived from the balance of human immunity and the mite pathogenicity. Demodicidosis has been reported in association with HIV infection. Rosacea like demodicidosis may be more frequent in HIV cases. However, a large clinical study of demodicidosis demonstrates that the overall incidence of demodicidosis mostly occurs in immunocompetent hosts. 21 One study showed that HLA-A2 phenotype had a protective role and the HLA-Cw2 phenotypes were susceptible to the mites. Either phenotypes could play their specific roles by regulating the end phase of the immune response. 21 a T cell co-stimulatory molecule a transcription factor that mediates interleukin-4 (IL-4) signaling Patients with a typical lesion of acne rosacea have CD4 + T cells in the dermal granuloma which infiltrate frequently around demodex parts. This finding suggests that a cell-mediated immune (CMI) response plays an important role in the pathogenesis of rosacea. 22 The mean DF mite density (MD)/cm 2 is significantly higher, and absolute numbers of lymphocytes, T-cell subsets and NK cells in the patientsû lesions is significantly lower than controls. It seems that the DF mites modulate the host CMI response to their advantage, and T-cell subsets and NK cells seems to be the target of immunosuppression. 22 The epidermis of the patients with demodicidosis undergoes lymphocytes apoptosis in parallel to the increasing mite density, this means-demodex may induce local immunosuppression to allow them to survive on the host skin. 23 Moreover, a study on plasma and secretory proteins showed that a novel function of IgD and serum protease inhibitors may act as a protective host response to the mite. 24 In veterinary medicine, the presence of the demodex mites has been correlated with immunodeficiency as evident in mice lacking CD28 and STAT6. This finding supports that commensal ectoparasites might contribute to disease when specific molecules required for an effective Th2 response are blocked. 25 In conclusion, the pathogenesis of demodicidosis is not fully understood; however, it is quite apparent that immunological response mediates development of skin lesion. Some mite antigens may elicit a delayed

4 33 Table 1 Clinical manifestations of demodicidosis Primary demodicidosis* 1. Demodicidosis A. Pityriasis folliculorum B. Demodex folliculitis C. Rosacea-like demodicidosis D. Demodex abscess E. Demodectic alopecia 2. Chronic blepharitis/seborrheic blephiritis Secondary demodicidosis** 1. Acne rosacea 2. Perioral dermatitis 3. Demodex infestation in immunocompromised host A. Demodex mites in AIDS patients (1) Pruritic papular eruption in AIDS (2) Folliculitis (3) HIV-related eosinophilic folliculitis B. Follicular hyperkeratosis spicules C. Basal cell carcinoma of the eyelid Remarks : *Primary demodicidosis represents the skin lesion caused by the mites as an etiologic organism. **Secondary demodicidosis represents the existing skin disease coexists with high prevalence of the mites. hypersensitivity reaction. A mite-derived lipase could also potentially release fatty acids from serum triglycerides which induces irritant reaction. They possibly have a pathogenic role only when present in high density and may be related to one of the following mechanisms 2,26 : 1. Blockage of pilosebaceous ducts due to reactive epithelial hyperplasia and hyperkeratinization 2. Mites serving as vectors for bacteria 3. A foreign body reaction to the mite 4. Induction of host immunity by the mites and their waste Clinical manifestations (See Table 1) Primary demodicidosis 1. Demodicidosis at the Institute of Dermatology, BKK during B.E., there were 266 cases of demodicidosis, consisted of 90 males and 176 females. All cases were defined by a compatible skin lesion and finding the mites more than 5/cm 2 on the lesion. Female was outnumbered male by two to one and the age range of most cases peaked around 35 years. Most Thai cases presented with erythematous itchy scaly patches with/without erythematous follicular papules on both cheeks (Fig.13A, B, C). Neither demodex species identification or aggravating factors was studied. This contrast to symptoms reported in Caucasian which the most frequent were follicular scales (71%) and telangiectasia (63%). 27 The immunocompetent children could present with erythema, papulopustules and variable edema of the face; and with a mild form resembling pityriasis folliculorum and a rosacea-like form. 9 Although there are several clinical variants of demodicidosis, a clear clinical classification is missing. The author prefers to categorize the clinical presentation of primary demodicidosis as below : A. Pityriasis folliculorum pityriasis folliculorum appears as facial erythema with fine follicular Data from Technology and Medical Informatics, Institute of Dermatology, BKK, Thailand

5 34 A B C Fig. 13 A, B, C Shows multiple erythematous itchy papules on both cheeks. (see colored picture p. 101) Fig. 14 Shows erythematous itchy patches with erythematous papules look alike mild case of acne rosacea. (see colored picture p. 102) plugs and scale producing a çnutmeg-grateré or çsandpaper-likeé appearance. It usually affects women and may be associated with itching and burning. B. Demodex folliculitis this entity may be associated with immune suppression. It presents as erythematous follicular papules and pustules on the face, often with a background of diffuse erythema. One case presented with an extensive and painful erythematous pustular lesion along the right face and scalp in a dermatome pattern clinically suggestive of varicella zoster. 32 Skin scrapings reveal numerous demodex mites. C. Rosacea-like demodicidosis severe demodicidosis may present with rosacea-like features in that there are papules and pustules. In contrast to Fig. 15 Shows early formed abscess intermingled with erythematous papules on both cheeks. (see colored picture p. 102) rosacea, this entity comes with sudden onset and rapid progression. There is follicular scaling with flushing and telangiectasia. Histologically, severe demodicidosis is characterized by follicular cysts with a granulomatous inflammatory reaction and numerous mites. (Fig. 14) D. Demodex abscess this type of lesion resembles severe granulomatous rosacea where the clinical expression depends on the degree of demodex infestation, duration, and the individualûs age and over all health. (Fig. 15) E. Demodectic alopecia human demodectic alopecia appears to be a real entity. This condition bears combination features of alopecia, erythema, and scaling. Large numbers of demodex mites are noted in biopsies or smears from affected follicles. The le-

6 35 sion is cleared after antimite therapy. 34 It was quite interesting that there was one report found the different between the clinical manifestation caused by DF and DB. The lesion induced by DF presents as erythematosquamous eruption on T-zone of the face. The rash started on unaltered skin and covered 8-15% of the face. Pruritus accompanied the onset of the rash, while erythema was first apparent after papulopustules were seen and disappeared after treatment. Half the patients showed seasonal exacerbations. The lesion caused by DB somehow showed more severe clinical features, as symmetrical malar papulopustular eruption. It developed on diseased skin and covered 30-40% of the face. Pruritus started after the lesion exacerbation, but erythema preceded the papulopustular phase and persisted after treatment. Most patients flared during the summer. 35 However, both DF and DB are always found together at a time in the pilosebaceous unit so how the researcher proved one of them as a pathogen is still quesionable. (authorûs comment-dr.wp.) Diagnosis a large number of the mites from suspicious lesions are essential in confirmation of diagnosis. Histological findings 28,36 in one large study of 388 follicles for the presence of histologic folliculitis revealed an association between folliculitis and demodex mites. The mites were found in 42% of follicles with inflammation, but in just 10% of the follicles without inflammation. Eighty-three percent of follicles containing demodex showed inflammation suggesting that demodex could preferential select inflamed follicles. 36 Biopsies of pityriasis folliculorum show a perivascular and diffuse dermal lymphocyte infiltrate without granuloma formation. The mites are present within pilosebaceous units. From rosacea-like demodicidosis, there is a primarily perifollicular infiltrate of mononuclear cells with possible granulomatous inflammation. The infiltrate is composed predominantly of CD4 + T lymphocytes, and perifollicular Langerhans cell may be found. In demodex abscess, there are granulomas with central necrosis (caseation) and foreign-body type multinucleated giant cells Chronic blepharitis/seborrheic blepharitis Demodex folliculorum of all stages is a common habitant of eyelid hair follicles and the lobules of the Meibomian glands. It is found in eyelid hair follicle about 26.7% of normal individuals. The mite is responsible for chronic eczematous blepharitis (çblepharitis acaricaé) with trichiasis and madarosis. 37 The incidence of mite infestation in the eyelash varied between 4%- 28.8% in patients with blepharitis. 38,39 This incidence increased with age; 100% of cases over age 70 years were involved. 40 The mites are also more abundant in persons with diabetes and associated with a scarcity of eye lashes in the lower lid. This association is independence of patient age. 41 The eye shows no pathologic change except for follicular distension and hyperkeratosis and occasional mild chronic perifolliculitis. 7 The adult

7 36 and immature mites consume epithelial cells, produce follicular distension and hyperplasia, and increases keratinization leading, in eyelashes, to cuffing consisting of keratin and lipid moieties. These changes as well as melanocyte aggregation are more extensive if large population of mites builds up in the follicles of the eyelid and destroys the Meibomian glandular cells, produces granuloma, plugs the ducts of the Meibomian glands thus affecting the formation of the superficial lipid layer of the tear film. Greasy scales on the lashes and foamy tears suggest seborrhea as well as demodicidosis. Cylindrical dandruff is pathognomonic for ocular demodex infestation. It is important to distinguish between cylindric casts (demodex-induced) and ordinary greasy scales on eye lashes and lid margin The eyelashes from whose lid margins cultured positive for S. aureus tends to have two or more mites than those without S. aureus. 41 Further studies may incriminate either or both demodex mites, in conjunction with other microorganisms, as transfer agents or synergists, or both, in producing ocular disease in man. Secondary demodicidosis Next, the well established skin conditions in which the mites are considered as a secondary, aggravating agent will be discussed. 1. Acne rosacea there are several potential causes including vascular abnormality, dermal matrix degeneration, environmental factors, and microorganisms such as demodex mites have been postulated in acne rosacea. The overall evidence is largely cir- cumstantial. It seems to be a disease of multifactorial origin. However, the clinical observation and histopathologic study suggest that the inflammation of the pilosebaceous follicle is a central pathogenesis of rosacea. 27 The mites may implicate as a causative role and individual immunologic response may modify the severity of the inflammatory response to them. 33 Rosacea most often appears as central facial erythema, telangiectasia, and often papules and pustules. This condition is characterized by episodes of remission and recurrence which can be divided into four stages 45 : Stage 1 : episodes of flushing (prerosacea) Stage 2 : persistent erythema and telangiectasia Stage 3 : papules and pustules Stage 4 : rhinophyma The major subtypes and variants of rosacea (Table 2) 46 The mites start to get involve in acne rosacea at stage 2. DF was detected in 86% of the cases. It was more frequently in cases with history of excessive use and/or prolonged use of topical steroids who later often developed epitheloid granulomas. 47 In such cases, erythema involves the whole of the application area and is usually associated with atrophy. Surprisingly, an unusual case of rosacea with maxillary sinusitis where the mites were found by a fine-needle aspiration, was also documented. 48 A study to assess DF pathogenesis in rosacea comparing females with papulopustular rosacea (PPR) with sex-matched normal volunteers,

8 37 Table 2 The major subtypes and variant of rosacea and their characteristics. 46 Subtype Vascular rosacea* (erythematotelangiectatic) Papulopustular rosacea* Sebaceous hyperplasia rosacea* (phymatous) Ocular rosacea* Granulomatous rosacea** * Major subtypes **Variant Characteristics Flushing and persistent central facial erythema with/without telangiectasia Persistent central facial erythema with transient, central facial papules or pustules or both Thickening skin, irregular surface nodularities and enlargement. May occur on the nose, chin, forehead, cheeks, or ears Foreign body sensation in the eye, burning or stinging, dryness, itching, ocular photosensitivity, blurred vision, telangiectasia of the sclera or other parts of the eye, or periorbital edema Firm, brown, yellow, or red cutaneous papules; or nodules of uniform size found that about 75% of them harbored the mites. The mean mite counts by site distribution were high on the cheeks, followed by the forehead and lastly the chin in both PPR and control groups. The total mean mite count in PPR cases was high initially and inclined after treatment. 49 If the clinical types of rosacea were considered separately, the mite density was statistically significantly higher than in controls only in the PPR type. Moreover, when compared with some other skin conditions like eczema and discoid lupus erythematosus, the mite was also significantly higher in the rosacea group. 34 These information supported a pathogenic role of the mite in PPR. In one study, demodex mites accidentally exposed to non-ablative IPL treatment for facial rejuvenation found coagulated and the author concluded that some esthetic improvement might be secondary to clearing of the mites and reduction of associated lymphocytic infiltrate. 50 Most cases of PPR had high demodex density 21 meanwhile some cases of rosacea might show normal number of the mite 51 ; in parallel, the mite can also highly present in many healthy individuals (some have mites over 5/cm 2 ). Although a certain mite density is not an appropriate criterion in the diagnosis of primary and secondary demodicidosis, a large numbers of DF may have an important role in the pathogenesis of rosacea, together with other triggering factors. 51 Additionally, a single data showed that lower quantities of lipids determined a higher incidence of DF in rosacea patients but this work was silently on exactly why and how this relationship occurred. It may be that the apparently increased population of demodex is a consequence rather than the cause of rosacea and at most, it may exacerbate the inflammation in predisposed individuals. 48 Histopathologic findings since the patients can present with a broad clinical spectrum, there is no specific histological features associated with rosacea or its clinical subtypes and variants. 52 Reflecting the clinical presentation, various pathologic changes

9 38 including organization of dermal lymphocytes into small nodular aggregates can be seen from case to case. Some papules demonstrate the association of granulomatous inflammation with damaged follicles, and the mites may be identified. The mite may induce the formation of a granuloma, but it is also possible that granulomas are consecutive to the destruction and resorption of hair follicles, and the mite being çdigestedé more slowly than the epithelial structures. 53 There is increase number of macrophages and Langerhans cell only in those subjects with a positive mite finding. The mites are found more number in inflamed follicles than noninflamed follicles. 28,36 Hair follicle infestation is associated with intense perifollicular infiltrate of predominantly (90-95%) CD4 + T cells. 28,36 Histological diagnosis of granulomatous rosacea is often extremely difficult because foreignbody granuloma reacting to the mites, keratin, sebum and ruptured cysts are very common on the face; the diagnosis should therefore be restricted to lesions that show clearly defined granuloma in an interfollicular distribution and in the appropriate clinical setting Perioral dermatitis this common eruption consists of discrete small pink papules, micronodules and pustules on an erythematous; occasionally scaling, base affecting the chin, nasolabial folds and the periocular region. 45 Its name originates from the distinctive location; appears symmetrically around the mouth with a clear zone of some 5 mm between the vermilion border and the affected skin. 54 It occurs almost exclusively in women whose age ranges between years old. 54 Only a few cases have been reported in children. 55 The lesion recurs over weeks to months. There is variably or no itching at all; however, an uncomfortable burning sensation may be present. Various environment sensitivities have been reported in individual patients but a generally applicable explanation is lacking. The condition seems to be etiologically linked in some cases to the use of potent topical steroids, some toothpastes, epoxy diacrylates in dental composite resins, foundation make-up along with moisturizer and night cream. 28 Perioral dermatitis together with cheilitis may be caused by flavoring agents in dentrifrices and gum, as well as fragrances, shellac, medicaments, and sunscreens in lipstick and lip balms. 56 An association has also been reported in renal transplant patients who on systemic steroids and azathioprine. 55 One of the possible etiologies links to perioral dermatitis is demodex mites. 28,57 Among those offensive agents; the use of fluorinated topical steroids of any usage forms : creams, ointments or inhalers, is the most frequently identified cause 54 and demodex mite density increased significantly with the duration of using topical steroids. 57 This relationship is possibly a secondary phenomenon. 57 Differential diagnosis some authors consider perioral dermatitis as a variant of rosacea while others consider the two entities to be distinct. 28 The two disorders occur in the same population although they differ clinically, and both respond to the same medications. Perioral dermatitis is histologically indistinguishable from rosacea. 45 It often appears in patients with vascular rosacea, but minimal malar

10 39 inflammation. So, the link to rosacea is not certain, but probable. Periorbital (periocular) dermatitis is a variant of perioral dermatitis occurring on the lower eyelids and skin adjacent to the upper and lower eyelids. Fluorinated topical steroids like the use of a steroid eye ointment have been implicated as the cause. 28 If intranasal inhaled steroids are used, a perinasal distribution may be seen. Prompt response to the same treatment employed in the perioral site is expected. 54 Histological findings this histological picture in perioral dermatitis is very similar to that of acne rosacea 55 but it tends to lack the dermal edema and telangiectasia characteristic of rosacea, and show more noticeable epidermal changes. 45 Like in acne rosacea, DF was isolated in mostly great numbers from lesions of the facial skin in patients with perioral dermatitis Demodex infestation in immunocompromised host Demodex folliculorum has been implicated in infections of the following immunocompromised host; patients with end stage renal failure, renal transplant, mycosis fungoides, non- Hodgkinûs lymphoma, leukemia and patient under chemotherapy, and AIDS In these immunocompromised hosts, demodicidosis may be more frequent and severe, and systemic therapy may be needed to achieve clinical resolution. Demodex mites can cause dramatic facial and eyelid inflammation as widespread erythema and scaling of the face and later pustules developed on the face and around the eyelids. They can also associate with bilateral blepharitis and lower lid chalazia. 10 Therefore, Demodicidosis should be included in the differential diagnosis of facial eruptions in immunocompromised patient of any age, and a standardized skin surface biopsy (SSSB) should be performed. 10,63 A. Demodex mites in AIDS patients HIV infects human helper T cells and leads to a progressive immunodeficiency disease. As much as 90% of the patients with AIDS and AIDS-related complex develop dermatologic problems. The skin lesions can be classified into three broad categories : infections, inflammatory dermatoses, and neoplasms. 64 It seems likely that in AIDS, demodex infestation does not manifest unless local or systemic immune function is altered, leading to the proliferation of the organism and subsequent disease At the stage which helper T cell range from cells/mm 3, acne rosacea may appear and once the helper T cell count is 200 cells/mm 3 or less hyperreactive skin and frequently, inflammatory, often pruritic skin diseases may appear. 64 Paradoxically, the conditions like eosinophilic folliculitis and enhanced reactions to insect bites may initially appear or be exacerbated by the sudden improvement of the immune status (the çimmune reconstitutioné or çimmune restorationé syndrome) that occurs with eradication of HIV viremia in a case on highly active antiretroviral therapy (HAART). 64 Pruritic papular eruption (PPE) in AIDS one of the most common skin problems in AIDS is a PPE reflecting of an abnormal host-cellular

11 40 immune response to an infective process. Numerous demodex mites were found in pustular lesions of PPE and the lesion resolved completely after a single overnight application of 1% lindane lotion. 65 It has been suggested that this may represent a hypersensitivity response to insect bites or DF infection. 66 Folliculitis histologic patterns of HIVrelated folliculitis can present as below 67 : (1) Acute folliculitis with bacteria and/or yeast (2) Lymphocytic perifolliculitis (3) Perifolliculitis with mixed inflammation (4) HIV-related eosinophilic folliculitis** (5) Follicular rupture with predominant granulomatous inflammation In these lesions a scattering of demodex mites is found but there is no single factor can be identified as the cause of HIV-related folliculitis, making antibacterial or antifungal therapy unlikely to be successful across a wide range of skin lesion in HIV patients. HIV-related eosinophilic folliculitis this chronic pruritic dermatosis characterized by discrete, smooth-surfaced papules located predominantly on the trunk and proximal extremities. The pathogenesis of HIV-related eosinophilic folliculitis is unknown. It has an autoimmune basis, with either the sebocytes or a constituent of sebum functioning as the autoantigen or it may be a hypersensitivity reaction to DF or Pityrosporum yeast. One case was associated with the use of forscarnet. The condition tends to manifest when the CD4 count is less than 200 cells/mm 3. 29,47,66 çeosinophilic pustular folliculitis (Ofujiûs disease)é which may be confused with this condition, has also been described in association with HIV and other diseases i.e. non-hodgkinûs and Hodgkinûs lymphoma, myelodysplastic syndrome, bone marrow transplantation 28, eosinophilic cellulitis, nevoid basal cell carcinoma syndrome. In addition, some cases of Ofujiûs disease can be induced by allopurinol, timepidium bromide, carbamazepine, after patch testing with minocycline and indeloxazine hydrochloride; and after prolonged treatment with oral corticosteroids in a patient with pustulosis palmoplantaris. 28,66 Histologic findings HIV-associated eosinophilic folliculitis is characterized by the presence of eosinophils and occasional small eosinophilic pustules in the outer root sheath or pilar canal of the hair follicle accompanied by a perivascular and interstitial lymphohistiocytic and eosinophil infiltrate in the superficial and deep dermis. 66 Differential diagnosis HIV-associated eosinophilic folliculitis is said to differ from Ofujiûs disease in that it has discrete intensed pruritic lesions but lacks arcuate plaques, palmoplantar lesions, and has fewer facial lesions. 68 Histologically, well-developed large eosinophilic pustules in the pilar canals are characteristic of Ofujiûs disease but are less common in **There are three major forms of eosinophilic folliculitis: eosinphilic pustular folliculitis (Ofujiûs disease), HIV-associated eosinophilic folliculitis and eosinophilic pustular folliculitis in infancy. (ref. 29)

12 41 HIV-associated eosinophilic folliculitis. 69 It is exceedingly difficult if not impossible to differentiate between eosinophilic folliculitis and suppurative (infective) folliculitis on clinical grounds in HIV-positive patients so skin biopsy is necessary. Features that may help to distinguish suppurative folliculitis in HIV-positive patients from HIVassociated eosinophilic folliculitis include an infiltrate dominated by neutrophils and macrophages, the presence of microorganisms amid the inflammation and rupture of the involved follicle. 28 In HIV-associated eosinophilic folliculitis, the small numbers of microbes (bacteria, yeast, Demodex spp.) were identified in 25% of the study biopsies in routine or special stains, but the organisms were away from areas of inflammation so were interpreted as nonpathogenic flora. 69 B. Follicular hyperkeratotic spicules (FHS) 70,71 FHS is a rare cutaneous disorder characterized by the presence of follicular, keratotic, horny spicules, mainly on the face. They have been described as idiopathic and associated with a variety of conditions i.e. chronic renal failure, Crohnûs disease and malignant diseases. The pathogenesis of FHS is unknown. Demodex mites may play a role in the etiology of this lesion, although this fact remains controversial. Interestingly, this condition reported to occur in immunocompromised hosts and it did not respond to permethrin and metronidazole. C. Basal cell carcinoma of the eyelid interestingly, one report revealed high number of demodex mites in patients with eyelid BCCs and they suggested that the mite may be one of the triggering factors of carcinogenesis in eyelid BCCs or predisposed people due to its traumatic/irritating effect or chronic inflammation. 72 However, the fact that the mite can be secondary in any existing pathological lesions of the face must also keep in mind, especially cancerous lesion which local immunity is defected. Laboratory investigations & techniques Morphology and biology of the mites The lifespan of DF is thought to be approximately 2 weeks (Fig. 16). The heart-shaped eggs hatch to produce hexapod larvae, and the eight-legged adults develop via two nymphal stages. 5 Follicle mites are quites mobile, and migrate from follicle to follicle. Transmission to infants probably occurs as a result of close maternal contact. 5 Light and ultramicroscopic findings Most infested follicles contain 2-6 mites, but occasionally they are much more numerous. 5 A survey done on healthy skin by SSSB under light microscope disclosed that all demodex mites are full-grown. Of these, 41% were ghosts. 73 The demodex mite has a flattened head, an elongated abdomen with four pairs of short, peglike legs. Demodex folliculorum measures mm in length, and has an elongated, striated abdomen giving it a worm-like appearance. Demodex brevis is shorter than DF. 20 Under scanning electron microscopy, DF assumes a head-down position in the follicle, often with the tip of the abdomen protruding from the follicular orifice (Fig. 17). The shape and size of the caudal extremity appeared to vary. The mouth-

13 42 Demodex life circle 60 hours Nymph Adult 12 hours Ovum Demodex folliculorum Side part Mouth Leg 60 hours Real body Demodex brevis Round vein Male length mm Female length mm Male length mm Female length mm 72 hours Protonymph Larva 36 hours Fig. 16 Lifecycle of Demodex spp. (from: Fig. 17 Under scanning electron microscopy, Demodex folliculorum assumes a head-down position in the follicle, often with the tip of the abdomen protruding from the follicular orifice. (see colored picture p. 102) parts of DF were composed of a complex set of structures, which included a round oral opening, a sharp oral needle, and a special hypostome that looked like a longitudinal spindle in the central position. On the end segment of palpus, there were seven strong Fig. 18 Shows the ultrastructure of the mouthpart of demodex (from: (see colored picture p. 102) palpal claws located on each side of the mouthparts (Fig. 18). DF had special piercing mouthparts, while the mouthparts of DB were a simple structure. There was no oral needle of DB, and there were only five pairs of palpal claws on the end segment of palpus. The offensive organs of demodex resulted in its pa-

14 43 thogenic effects. 74 Laboratory technique Under an ordinary light microscope, a few simple techniques can be used to identify the demodex mites harvested from skin lesion. In the circumstances, if fluorescence microscope and polarized light microscope are available the physician can perform more highly sophisticated techniques to identify the mites. 1. Standardized skin surface biopsy (SSSB) this technique uses cyanoacrylate gel to sample the horny layer and follicular content. The technique and interpretation of positive result may be slightly different from paper to paper because there is no consensus on the detail of the lab protocol. Based on many reports, using SSSB, DF mite more than 5/cm 2 is found in most pathological skin lesions. 34,51 However, the observation of a clinical case demonstrates that, in contrary to what was presumed before, a single SSSB can fail to collect the complete biotope of the mite thus gives false negative result. 75 Hence, a five SSSB is recommended to take from each case and the determination of five and more living parasites/cm 2 area is set as a positive result. 18,51,58,63,72,76 (Please read the detailed labs technique practicing at the Institute of Dermatology, BKK in page 51). This method could be a useful diagnostic tool to diagnose for demodecidosis, with a 98% specificity when demodex density is higher than 5/cm Actually, some patients with demodicidosis has the mite less than 5/cm 2, on the other hand, some normal individuals have mite more than 5/cm Therefore, the correlation of a positive result and clinical manifestation is essential for diagnosis. In sum, to confirm diagnosis of demodecidosis in any clinical setting, the physician can rely; A. Finding of DF mite more than 5/cm 2 in the skin sampled by SSSB. or B. Presence of 5 or more mites in scale with 40% KOH under a single low-power field Follicular biopsy 77 this is an extension of the noninvasive çsssbé method. A quick-setting cyanoacrylate polymer is used to extract the contents of sebaceous follicles. The retrieved material can be examined histologically at the light or electron microscopic level. By follicular biopsy, many types of analyses may be performed; microbial density, lipid components (acne), mite population (Demodex), hair retention (trichostasis), penetration of topical drugs and chemicals, localization of enzymes, etc. Thus, this technique is useful for studying the contents of sebaceous follicles in health and disease including demodicidosis. 3. Modified KOH dissolution technique using Tween the technique has been developed for the diagnosis and quantitative evaluation of ectoparasitic mites of veterinary importance and yields in very high a positive result. We believe this method can be applied in confirmation of human demodicidosis. 4. Fluorescent microscopic technique 79 the technique can be rated as a useful enrichment of the diagnostic potential in particular for laboratories with a large number of submitted skin scrapings because using this technique helps in reducing in evaluation

15 44 time. Furthermore, it can clearly distinguish the mite from other microorganism like dermatophytes and yeasts and the technique is easy and quick. Moreover, the fluorescent stain solution keeps sufficiently long. 5. Staining with alkaline Congo red viewed in polarized light 80 When viewed in polarized light, the kitin envelope of the mite exhibits a green birefringence of the same quality as amyloid. The mites can also be visualized more specifically by staining with alkaline Congo red. This technique can be used in cases when a differentiation between a mite and other structure of skin is difficult. Transmission Demodex is transmitted from human to human through skin contact. They are found abundant (58.2%) in dust from mattresses of different composition and age. The dust from the cotton-horsehaired mattresses had a significantly higher allergenic activity than from those of polyester-foam. 81 The information on transmission and survival of demodex outside the body are helpful to explore the relationship of demodex and skin diseases. Unfortunately, there is no study about the prevalence and other mite-related aspects on personal material of different kinds used by Asian people. Only one report that could prove the transmission of Demodex canis to a boy with intense irritation and dermatitis, somewhat resembling that produced by scabies developed after contacting with a dog. The mite was recovered from a boy and his pet dog and the lesion was successfully treated with permethrin. 82 Studying on a dog model shows that D. canis may have host preference but not strict host-specificity. 83 Demodex mites as a vector of other microorganism infections Here comes the question whether demodex mite acts as a vector of a disease. At least, there is documented evidence that numerous demodex mites containing inside them spores of Microsporum canis 5 ; and Mycobacterium leprae. 31 Mycobacterium leprae can also be found on the mite skin. 31 The mite has the potential to ingest various microorganisms that are found in its niche and transport them to other areas of the skin or possibly to other individuals. 84 However, this evidence is not strong enough to accuse of them for transmitting pathogenic organism from a person to another. Demodex infestation in other mammals Other Demodex spp. have also been identified in the hair follicles of many other mammals such as dogs, cats, goat, cattle, rhesus, koala bear, hamster etc. and can cause skin lesions on their hosts as well The immunological response to demodex mite in animal seems to be like in human and the infection shows high prevalent in the immunocompromised host Treatments for demodex infestation The adequate therapy for diseases of pilosebaceous gland origin includes rosacea, gram-negative folliculitis, demodex folliculitis, perioral dermatitis as well as seborrheic dermatitis requires the basic knowledge of

16 45 pathogenesis and clinical differentiation. Unfortunately, topical steroids are often prescribed for these diseases, resulting in well-known corticosteroid side-effectsskin atrophy, telangiectasia and secondary demodicidosis. Demodicidosis remains a diagnostic and therapeutic challenge. Treatment of the eruptions in which demodex has been implicated consisted of applying the topical medicament twice a day till the lesion clear. The recommended treatments are permethrin, sulfur, lindane, benzyl benzoate, benzoyl peroxide, topical/ oral metronidazole. 9,10,31,58,62,82, Antiparasitic therapies used against lice or scabies may fail in control of the mites. Refractory cases may require oral ivermectin. Oral administration of 250 mg metronidazole 3 times a day for 2 weeks seems to work in the patient with chronic mite infestation whose skin condition fails to oral administration of ivermectin and external application. 31 Tetracycline shows no effect on demodex mite and shows controversial efficacy in acne rosacea. 48,112,113 The duration of treatment depends on the clinical response; however, based on a study with 0.25% hexachlorocyclohexane (Jacutin) the average treatment duration is a week for primary demodicidosis, for 7 weeks for rosacea and 5 weeks for perioral dermatitis. 114 Combination treatments 15,31,76,109 can be also tried in some cases such as application of diluted camphor oil with glycerol and 500 mg metronidazole orally 76, oral 200 µg/kg ivermectin with subsequent weekly topical permethrin showed impressive treatment efficacy in a severe and a recalcitrant case. 15,107 In some patients with eosinophilic folliculitis which demodex mites are suspicious as the antigenic trigger, repeated applications of permethrin (every other night for up to 6 weeks) may be of benefit. 64 Conclusion Demodex mite is a commensal that occasionally exerts a pathogenic role. Nowadays in daily practice, demodicidosis is found increasingly among Thai patients. Both normal and immunocompromised hosts are infested. The mite is proved to be the primary cause in several skin conditions and acts as opportunistic organism in some other dermatologic diseases. A few simple laboratory techniques under light microscope such as standardized skin surface biopsy (SSSB), follicular biopsy and modified KOH dissolution technique using Tween 80 are recommended to confirm diagnosis for demodicidosis. Furthermore, laboratory techniques using alkaline Congo red stain and special microscope like fluorescent microscope and polarized light microscope can be useful in confirmation of demodicidosis. Demodicidosis is diagnosed when the mite density is higher than 5/cm 2 by SSSB or more than 5 mites in scale with 40% KOH examined under a single low-power field. Most cases of demodicidosis respond well to a number of topical treatments such as benzoyl peroxide with/without erythromycin, benzyl benzoate, gammar benzene hexachloride, metronidazole, permethrin, and oral ivermectin. A combination of topical and oral antimite medications can be tried in recalcitrant cases. Special consideration in diagnosis and treatment for demodicidosis is required when a physician faces with an immunocompromised host.

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