INFESTATION OF THE SKIN WITH DEMODEX

INFESTATION OF THE SKIN WITH DEMODEX FOLLICULORUM ROBERT L. BRECKENRIDGE, M.D. Department of Pathology and Clinical Laboratories, Jefferson Medical College, Philadelphia 7, Pennsylvania Demodex folliculorum is a common parasite of the human skin. Since its discovery by Simon in 1843, it has been reported in hair follicles, meibomian and sebaceous glands, involving particularly the face, nose, lips and forehead of man and some domestic animals. 4 A number of lesions have been ascribed to this mite, including acne, comedones, senile keratosis, chalazion, blepharites and even epitheliomas. 6 Borrel 3 even believed that D. folliculorum played an important role in the transmission of leprosy. This parasite has also been said to produce demodicidosis, 7 a specific lesion of the scalp, and pityriasis folliculorum (Demodex). 1,2 Garven 6 suggested that it may be a factor in the production of 'sore nipples. The majority of authors, however, refute the pathogenicity of the parasite. Demodex folliculorum is a microscopic mite, measuring about 400 microns in length 9 and having an elongated, transparent body with 8 stumpy, molelike legs which have 3 joints (Fig. A). The capitulum is short and trapezoidal in shape. The mandibles and maxillae are styliform, and the palps are closely applied on the lower surface of the head. The abdomen is transversely striated circumferentially and tapers to the posterior rounded end. Respiratory organs are absent. The male sexual organ is well developed and usually projects from the genital orifice on the dorsal surface of the cephalothorax in the interval between legs I and II. 10 The introitus of the female is a longitudinal slit at the anterior end of the ventral side in front of the last pair of legs. The female lays eggs that are fusiform in shape, transparent, thin-shelled, and measure 75 by 35 microns. The capacity of the female for laying eggs has not been determined. 10 A 6-legged larva hatches from the egg and develops into an 8-legged adult after 4 moltings. It lives with its head directed internally in the hair follicles and sebaceous and meibomian glands. As many as 200 have been counted in 1 hair follicle. Usually more than one follicle is infested. Fanthom 6 estimated that they are present in the skin of half the population including children, particularly in the normal borders of the eyelids. They are not found in infants. The mode of transmission is not well understood. The present study was undertaken to establish the morphologic characteristics of the mite in tissues and to clarify the importance of this ubiquitous parasite in the production of symptoms and various skin diseases. MATERIAL A total of 1435 skin biopsies, which had been seen in our laboratory during the past 4 years, was examined for D. folliculorum. Except for special stains, Received for publication December 13, 1952. Dr. Breckenridge is Associate Director of Clinical Laboratories. 348

INFESTATION AVITH DEM OBEX FOLLICULORUM 349 only those sections Avere studied AA'hich Avere stained originally Avith hematoxylin and eosin. Usually only one slide Avas made from a single case. The majority of the lesions in AA'hich the mite was seen Avere epitheliomas (86), sebaceous cysts (19) or nevi (40), the 3 most common skin biopsies in our hospital. The remaining sections included a variety of skin diseases. The recognition of D. folliculorum is based upon the morphologic characteristics of the mite in the skin. The cuticle of the mite may be mistaken for keratin, but it has transverse striations and the body has a definite contour (Fig. A). Frequently leg and head parts are present. The blue-staining germ cells are quite characteristic and are seen more readily in cross-sections (Fig. B). They are smaller and less regular in outline and staining qualities than Pityrosporum ovale Avith Avhich they might be confused. 8 After a little practice, the mites are easily identified on scanning the section Avith the IOAV poaver of the microscope and searching the hair follicles and sebaceous or meibomian glands. Because most arthropods contain glycoprotein, the Hotchkiss-McManus stain was used in examining some of the sections. The vermiform mite took a positive stain and stood out clearly from the surrounding tissue (Fig. C). This stain proved to be ideal for studying the mite, but is not required for its identification. RESULTS Distribution. Demodex folliculorum was found in 186 skin sections of 1435 examined. It Avas found most commonly on the face (146), especially about the nose (37 of the 146), AA'here sebaceous glands are most numerous, and also on the neck (8), thorax (15), buttock (2) and penis (1). Fourteen of the sections Avere not specified as to site of excision. None Avas found in biopsies from the extremities. Of interest Avas the presence of D. folliculorum in the circumcised foreskin removed from a 70-year-old man. The specimen also shoaa'ed erythroplasia of Queyrat. Another interesting instance Avas the discovery of the mite in the skin overlying a pilonidal cyst. Careful search failed to reveal the presence of the mite either in this pilonidal cyst or in others examined. This Avas analogous to the findings in the sebaceous cysts studied. D. folliculorum Avas seen in 7 of 32 sections of nipple examined. It Avas found in the sebaceous glands and rarely in the main collecting ducts near the surface. There Avas no dilatation, inflammation or other evidence of disease in the area adjacent to the mite. Pathologic changes. The mite AA'as always seen AA'ith its head directed internally in the hair follicles alongside the hair shaft. Its presence produced dilatation of the follicle and obstruction to the normal AOAV of sebum over the shaft and the cutaneous surface. The hair*shafts Avere broken off, and the epidermis adjacent to the infesting mite Avas hyperkeratotic. The mite Avas encased in a sheath of keratin Avhich frequently projected above the surface as a small excrescence (Fig. D). The histologic changes often simulated those seen in comedones and acne. In some sections the mite AA r as contained in an epithelial-lined cyst in Avhich the hair shaft greav in a curled manner. In a few cases the parasite Avas

350 BRECKENRIDGE associated with a fibrous tissue and lymphocytic reaction in the adjacent dermis (Fig. E). Some of the mites were found in the sebaceous and meibomian glands, where they apparently fed directly on the fat-laden cells (Fig. B). D. folliculorum was found in the adjacent hair follicles and sebaceous glands in 19 of 376 biopsies of sebaceous cysts, but in no case was it found in the cyst proper. In several instances the sebaceous material from freshly submitted tissue was examined directly for the mite but none was found. The parasite was found also in the adjacent skin appendages in 86 of 434 epitheliomas and in 40 of 414 nevi. In no instance was the organism seen in the tumor. The affected skin frequently was the seat of hyperkeratosis, atrophy of the epidermis and basophilic degeneration and fragmentation of the collagen. Symptoms. In an attempt to learn whether or not D. folliculorum could produce symptoms, the histories were examined of those patients in whom the biopsy revealed no other dermal disease. The most common complaint in the 17 histories examined was the presence of a small raised area. Some of the patients stated that the lesion slowly increased in size and had been present for a long time. In several patients the raised area was associated with erythema or scaling. Itching was not common, only one patient complaining of intense itching and in this patient it was believed that the itching was related to the primary disease of polycythemia vera. The biopsy had been taken at random from the back of the chest. In the histories of 5 patients no symptoms were listed. DISCUSSION The mites which lodge in the hair follicles not only cause dilatation of the follicle but also may act as a barrier to the normal flow of sebum. The lack of the lubricant may result in fragmentation of the hair shafts and hyperkeratosis. Occasionally a plugged follicle leads to formation of a cyst lined with epidermis and containing the mites as well as the fragmented hair shaft which continues to grow in a curled manner. The projection of the capsule-like sheath of keratin surrounding the parasites above the skin surface produces the nodule, which becomes apparent to the patient. The inflammatory reaction, when it occurs, may produce slight erythema. FIG. A. Semidiagrammatic drawing and photomicrograph of Demodex folliculorum showing elongated, transparent body with 8, short, molelike legs, mouth parts, transversely striated abdomen and, in the drawing, longitudinal, slitlike introitus caudad to the last pair of legs. (Slide preparation by courtesy of Dr. W. G. Sawitz.) X 900. FIG. B. Photomicrograph showing cross-section of a mite in a sebaceous gland. The blue-staining germ cells may be identified in the center of the body. The mite is frequently seen in cross-section deep within the sebaceous gland. X 100. FIG. C. Longitudinal section of 2 mites lying parallel with their heads directed internally. They stain brilliantly purple-red with the Ftotchkiss-McManus stain. Note moderate round-cell infiltration in perifollicular zone. X 50. FIG. D. Longitudinal sections of several mites in a dilated hair follicle. The skin shows atrophy of the epidermis, basophilic degeneration and fragmentation of the upper portion of the dermis and mild perifollicular fibrosis and round-cell infiltration. Note that the caudal portions of the mites project slightly above the skin surface and are surrounded by keratin. X 50. FIG. E. A dilated, blind hair follicle containing an ingrown hair and one or more mites surrounded by keratin. There is moderate round-cell infiltration in the perifollicular zone. X 50.

FIGS. A-E 351

/ 352 BRECKENRIDGE The mite can readily be identified, in a careful examination of the hair follicles and the collecting ducts of nipples, by finding the longitudinal, eosinophilic body having a definite contour, transverse striations, and frequently leg and head parts. The blue-staining germ cells and head parts are more commonly seen on cross-section, buried among the fat-laden cells of the sebaceous or meibomian glands. It is unlikely that D. folliculorum can cause epitheliomas, sebaceous cysts, nevi, pilonidal cysts or carcinoma of the breast. It is not seen in the center of these lesions but rather in the adjacent skin appendages. It probably more readily enters and survives in diseased skin than in normal skin. This would account for its frequent occurrence in these lesions as well as in skin showing hyperkeratosis, atrophy of the epidermis and degeneration of the collagen. Since the material did not include patients with demodicidosis or pityriasis folliculorum (Demodex), it was not possible to confirm the findings of Miskjian 7 and Ayres and Anderson. 1 ' 2 The absence of inflammation in sections of 7 invtfested nipples examined did not substantiate the suggestion of Garven 6 that the mite is a factor in the causation of sore nipples. ' ; SUMMARY K......j;. "Demodex folliculorum was found in 186 of 1435 skin biopsies. The parasite was readily identified by the ordinary hematoxylin and eosin stains. The Hotchkiss-McManus stain colored the parasite purple-red and contrasted it well from j^the surrounding skin. The infestation was limited to the hair follicles, sebaceous Sr or meibomian glands, involving particularly the face, nose, lips, forehead and the main collecting ducts in the nipple of the breasts. It is believed that infestation by the mite may lead to formation of ingrown hairs, dilated hair follicles and comedones, but that it does not produce sebaceous cysts, epitheliomas, carcinoma of the breast, nevi or pilonidal cysts. Demodex folliculorum may produce no symptoms or visible manifestations, or it may produce a slightly raised, firm, nodule in the skin, occasionally erythematous and scaly, which may enlarge slowly over a long period of time. REFERENCES 1. AYRES, S., JE.: Pityriasis folliculorum (Demodex). Arch. Dermat. & Syph., 21: 19-24 1930. 2. AYRES, S., JK., AND ANDERSON, N. P.: Demodex folliculorum, its role in the etiology of acne rosacea. Arch. Dermat. & Syph., 25: 89-98, 1932. 3. BORREL, A.: Precis de Parasitologic. Ed. 3. Edited by E. Brumpt. Paris: Masson et Cie. Vol. II, 1949, pp. 1207-1208. 4. CRAIG, F. C, AND FAUST, E. C: Clinical Parasitology. Ed. 5. Philadelphia: Lea and Febiger. 1951, p. 676. 5. FANTHOM, H. B., STEPHENS, J. W. W., AND THEOBALD, F. V.: The Animal Parasites of Man. New York: Wm. Wood & Co. 1915, p. 708. 6. GARVEN, H. S. D.: Demodex folliculorum in the human nipple. Lancet, 2: 44-45, 1946. 7. MISKJIAN, H. G.: Demodicidosis (demodex infestation of the scalp). Arch. Dermat. & Syph., 63: 282-283, 1951. 8. NICHOLAS, L.: Demodex folliculorum, its incidence in routine histologic study of the skin. Arch. Dermat. & Syph., 47: 793-796, 1943. 9. PATTON, W. S., AND CRAGG, F. W.: A Textbook of Medical Entomology. London: Christian Literature Soc. for India, 1913, p. 695. 10. PATTON, W. S., AND EVANS, A. M.: Insects, Ticks, Mites, and Venomous Animals of Medical and Veterinary Importance, Croydon: H. R. Grubb, Ltd. 1929, p. 328.