Silicosis and tuberculosis Silicosis and concomitant tuberculosis: the rad iolo

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1 Silicosis and tuberculosis Silicosis and concomitant tuberculosis: the rad iolo ALBERT SOLOMON, PROFESSOR EMERITUS, DAVID REES, MARIANNE FELIX, AND ENGELA VENTER A proposed radiographic classification of tuberculosis to accompany the ILO International Classification of Radiographs of Pneumoconioses OCCUPATIONAL MEDICINE SECTION NATIONAL CENTRE FOR OCCUPATIONAL HEALTH (NCOH) BOX 4788 JOHANNESBURG 2000 TEL: FAX: ventee@health.gov.za PERMISSION TO PUBLISH THIS ARTICLE, WHICH ORIGINALLY APPEARED IN THE INTERNATIONAL JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HEALTH 2000; 6: , IS REPUBLISHED WITH KIND PERMISSION FROM THE EDITOR, JOSEPH LADOU. THE INTERNATIONAL JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HEALTH IS PUBLISHED BY ABEL PUBLICATION SERVICES, INC AQUINAS COURT, BURLINGTON, NORTH CAROLINA ABSTRACT A significant proportion of workers exposed to silica dust are at risk to develop tuberculosis (TB). The higher the International Labour Organisation (ILO) category of silicosis the greater the TB risk. Subtle radiographic presentations of TB may be the initial manifestation of TB, particularly in the absence of sputum identification of TB bacilli. A proposed TB X-ray reading form in addition to the ILO categorisation of silicosis is offered. The implementation of a standardised TB X-ray reading approach should alert the clinician to indolent TB lesions. INTRODUCTION The prevalence of active or inactive pulmonary tuberculosis (TB) is high in former and current gold miners in South Africa. Cowie (1994) followed a cohort of 1153 gold miners for seven years and concluded that of the 818 of these men with silicosis, one quarter would have TB by the age of 60 years. 1 Trapido, et al. conducted a survey among 238 former goldmine workers in the Eastern Cape; the prevalence of radiological evidence of TB was recorded as 33% and 47% by the two readers, respectively. 2 Several epidemiological factors influence the incidence of tuberculosis in silica-exposed workers. It is generally agreed that the point prevalence of TB in the general population plays a role in determining the incidence of the infection in patients with silicosis. 3 A South African autopsy-based study of black miners indicates an increased incidence of tuberculosis associated with silica exposure and increasing length of service. 4 Gold miners at high risk for TB can be identified by age, mining occupation, silicosis status and HIV infection. 5 However, with radiological evidence of silicosis, patients have a greatly increased incidence of tuberculosis. Additionally, the silica dust that miners accumulate in their lungs during exposure remains a lifelong risk factor for the development of pulmonary TB. 6 Even after their exposure to dust end, ex-miners continue to be at risk of developing silicosis, and have an increased risk of developing pulmonary TB. 7 The use of sputum staining and culture is the major modality for the detection of active TB in miners and other silica exposed workers. Where sputa remain persistently negative for TB, the chest radiograph becomes extremely important in the handling of workers suspected to have active infection. THE NEED FOR AN X-RAY READING FORM SPECIFIC FOR TUBERCULOSILICOSIS A grading system has been established for radiographic evidence of TB (see appendix on page 6). The tubercle bacillus invades the respiratory tract via the bronchial pathway. In the main the pathological lesions remain in contact with the airways. Recovery and identification of the TB organism are dependent on this airway contact. However, when TB manifests as an interstitial compartment pathology, i.e. miliary pulmonary TB; localised and isolated, often satellite, interstitial granuloma; or profuse nodular interstitial TB, the recovery of the organism may not be possible. In this situation, diagnosis depends on the clinical presentation. In the case of indolent pulmonary TB with little clinical activity, the radiographic changes of pulmonary TB may be the only indication of pending problems. When silicosis is complicated by interstitial nodular TB, heavy reliance is placed upon the radiographic differentiation and identification of the two entities. The recognition of an aberrant radiographic pattern may alert the clinician to the presence of an indolent TB lesion despite lack of symptomatic support or sputum recovery of the TB organism. The need for a standard approach in order to diagnose TB in individuals, to measure the extent of radiological evidence of TB, and for epidemiological purposes, is paramount. Standardising radiograph reporting in TB will enhance comparability and facilitate the monitoring of cohorts; and make a useful contribution to epidemiologic investigations and medical surveillance. An experienced reader of the occupational chest radiograph, if without formal radiological training, is probably not conversant with the subtleties of radiologic 4 JULY/AUGUST 2003

2 rad iologist s enigma signs of TB in the presence of silicosis. Nodular tuberculosis and silicosis in their interstitial compartment manifestations are radiologically indistinguishable. Additional radiographic features, often subtle, have to be carefully searched for and recognised if the correct radiologic conclusion is to be reached. Given the morbidity and mortality associated with TB, it has become essential to be rigorous when assessing the chest radiograph of the silica-exposed worker to ensure that the radiologic diagnosis of TB is not missed. THE RADIOLOGY OF NODULAR TUBERCULOSIS AND ASSOCIATED SILICOSIS Of importance to note is the finding that where there is no quartz exposure, the profuse nodular configuration of TB rarely occurs. Reviewing the archives of a local tuberculosis hospital revealed only three cases of profuse nodular TB over a two-year period (Dr M. Andre, personal communication). However, when quartz exposure has occurred, a nodular form of pulmonary TB manifests. 10 Silicosis in its progress exhibits a regular even nodular bilateral profusion on the chest radiograph. The nodules are usually round and regular, irregular opacities being less common. Nodular TB presents with a localised aggregation in a much shorter time than silicotic nodules. A marked variability and even irregularity in nodular size is not unusual in the presence of TB. The nodular form of TB in the presence of silicosis becomes noticeably linear, often taking a distinct position along the broncho-vascular bundle. In the case of profuse nodular silicosis and associated tuberculosis there is often a chronological mismatching, i.e. earlier onset than expected or more rapid progression of the radiographic changes. In the region associated with this linear arraignment a prominent hilar flare becomes evident. 10 Unexpected supraclavicular changes may alert the chest radiograph reader to the presence of tuberculosis. These radiographic differences should alert the clinician to the presence of an indolent TB lesion. This is important where the identification of the TB organism is not forthcoming in the sputum. MINIMAL CHANGES RELATED TO TB Previous-onset TB followed by silica exposure, i.e. tuberculosilicosis, requires the radiologist to correctly assess the minor, as well as florid, changes of established pulmonary TB. Obvious pulmonary architectural distortion, manifested by broncho-vascular-bundle and mediastinal distortion, fibrotic bronchiectasis, and volume loss, as well as JULY/AUGUST

3 evidence of parenchymal or nodal calcification, offers little difficulty in recognition. It is likely that these local confined changes will not hamper categorisation of profuse silicotic nodulation in the remaining lung fields. More subtle pulmonary vascular pattern disruption (cicatrisation) and cicatrisation bullae with a sparse profusion of localised nodular TB granuloma will remain an area of contention until disciplined agreement in recognising parenchymal changes likely to be attributable to TB can be achieved. The separation of nodular silicosis from granuloma in this situation remains controversial. It is the authors suggestion that these cicatricial changes plus nodules are best interpreted as likely TB granulomas, requiring careful future monitoring when the worker is in a high silica dust occupation. OVERT EXTENSIVE TB Overt TB, i.e. cavitary, subsegmental and segmental opacification, bronchogenic dissemination and pleural and pericardial involvement, usually offers little diagnostic difficulty to the experienced chest radiograph reader. Problems arise with the concomitant interstitial manifestation of TB and silica nodulation. CONSIDERATIONS IN DEVELOPING A STANDARDISED TB REPORTING FORM The radiographic categorisation of the chest changes found in TB will necessitate the same disciplined approach for the radiologist as has the International Labour Organisation (ILO) Classification of Pneumoconioses. 8 Loose pathological terminology, e.g. fibrotic changes has no place in radiological reporting. A correct descriptive assessment is essential to justify the use of pathological terminology. We propose that a standardised TB reporting form be an optional addition to the ILO pneumoconiosis X-ray reading form and that a scoring system for grading the radiological extent of TB be included as part of this standardised reporting form. A standardised approach will draw the reader s eye to the sometimes subtle TB changes and provide a system upon which to view secular changes. CHRONOLOGICAL DETAILS: AN AID TO TB DIAGNOSIS A standardised X-ray reading form will not negate the need for a good history in assessing individual cases. Vital information is needed for a reliable assessment of the chest radiograph. This includes an employment history, duration of exposure, incidents of excessive exposure, age at initial exposure, age at presentation of radiographic changes, and the patient s ethnic group. The duration and the silica residence time since first exposure are critical in the radiographic assessment of workers exposed to silica dust. Radiologic evidence silicosis is less prevalent with less than seven years of exposure, unless the environment is heavily Appendix: TB GRADING a. The following well-validated US National Tuberculosis and Respiratory Disease Association grading system has been widely used for assessing the extent of radiographic involvement by tuberculosis. Four grades are defined as follows, based on careful review of standard 6 foot upright posteroanterior film, with or without lateral projection. The interpreter s grading is indicated as an integer (0-3) or by writing the descriptive grade, i.e. normal, minimal disease, moderately advanced. b. Number of lung zones involved by disease ( zone score ) The zone score is the number of lung regions (0-6) involved by disease (infiltrate, cavity or effusion). Each lung is divided into three zones (upper, middle and lower) by dividing the distance between the apex of the lung and the ipsilateral hemidiaphragm (measured with a ruler) by 3. The zone score is the number of lung zones where visible disease is present and is recorded as an integer (0-6). Grade no. Descriptive Grade Definition 0 Normal No visible intrathoracic radiographic abnormalities suggestive of TB. 1 Minimal disease Infiltrates of slight to moderate density; disease may be present in a small portion of both lungs; the total volume of the infiltrate(s) must be the volume of one lung present above the second costochondral junction and the spine of the fourth or the body of the fifth thoracic vertebrata; no cavitation may be present. 2 Moderately Disease may be present in one or both lungs; the total extent must advanced disease not be more than the following: a. Scattered lesions of slight to moderate density may not involve more than the total volume of one lung, or the equivalent volume of both lungs. b. Dense, confluent lesions may not involve more than _ of the volume of one lung. c. The total diameter of cavity(ies) may not be >4 cm.* 3 Far advanced Lesions more extensive than moderately advanced. * Use a ruler to measure diameters of cavities Source: Classification of pulmonary tuberculosis. In: Diagnostic Standards and Classification of Tuberculosis. New York: National Tuberculosis and Respiratory Disease Association, 1969; JULY/AUGUST 2003

4 contaminated, e.g. sand blasting or in uncontrolled mines. Furthermore, initial radiographic changes are less prevalent in workers less than 40 years old. However, it should be noted that a review of 217 cases has revealed high levels of silica exposure in workers in the non-mining industry on the Witwatersrand, as evidenced by the high proportion of cases with massive fibrosis (21%); patients less than 40 years old at diagnosis (21% of blacks); and patients exposed for less than 10 yrs (18%). 9 There was a close correlation between years of silica exposure and the prevalence of silicosis. There was also an effect of silica residence time in the lung. Despite cessation of exposure, changes may belatedly appear long after the initial years of exposure. 7 A PROPOSAL Following the ILO categorisation of the silica opacities (which is usually not possible in the presence of widespread TB dissemination), it is suggested that the presence of TB be recorded using the complementary TB reading form (Figure 1 on page 8) and glossary (Table I below). The present practice of recording silicosis and TB, or TB and silicosis, and with no determination of a silicosis category, is to be avoided if possible. The value of the proposed TB TABLE I. GLOSSARY OF TERMS DESCRIBING THE TB LESIONS Extensive disease: C P S BA M N Established lesions: Nod Cic FibBr cavity patchy opacification segmental (pneumonic/lobar) broncho-alveolar (acinus rosette) miliary nodal nodules cicatrisation fibrotic bronchiectasis (bronchovascular bundle distortion with bronchiectatic changes) Established lesions (cont.): Cbul cicatrisation bullae (hairlike bullae in the presence of vascular bed distortion) CPOb costophrenic sulcus obliteration FvolLoss fibrotic volume loss FibCv fibrotic cavity FibNod fibro-nodular HD hilar distortion TD tracheal deviation O other TB plus silicosis: LNA linear nodular arraignment HF hilar flare XF excessive profusion SASOM ANNUAL CONFERENCE Kopanong Conference Centre and Hotel, Benoni 5 and 6 September 2003 Ethics in health a comprehensive perspective This conference offers you the knowledge, understanding and guidelines to manage ethical issues in your work, whether it is in the public or private sector, in the workplace or consulting rooms. Topics will cover issues that are relevant to all the parties involved, including employers, employees, colleagues, trade unions, the State and legal professionals. Please book early, as seats are limited. Contact: Michelle Shelby Tel: /1 sasomdm@iafrica.com JULY/AUGUST

5 FIGURE 1. TB X-RAY READING FORM 8 JULY/AUGUST 2003

6 reading sheet will have to be assessed, e.g. by the radiographic assessment of workers with a postmortem correlation of the pulmonary findings. Alternatively, validation of the suggestive radiological features of TB could be assessed by follow-up of cases for manifestation of active disease. Consideration should also be given to the importance of training in the use of the X-ray reading form and continuing quality assurance. USE OF THE COMBINED X-RAY READING FORMS The initial X-ray reading form follows the standard International Labour Organisation classification. 8 The protocol for assessing the radiograph follows ILO instructions. Any radiographic change of a lesion suspected to be TB would call for the additional reading classification. In the case of widely disseminated bronchogenic TB the classification of silicosis would be in doubt. CONCLUSION Given the tremendous problem of silicosis complicated by TB in the gold mining industry of South Africa, it has become mandatory to explore all avenues in order to tackle the problem at the source. This paper proffers a detailed TB X-ray reading form as a disciplined aid in recognising the protean manifestations of pulmonary TB. Aberrant nodular patterns may be more easily recognised and alert the chest X-ray reader to the presence of associated indolent TB, which, when unrecognised, places the individual at risk and compounds the problem of control. REFERENCES 1. Cowie, R.L. The epidemiology of tuberculosis in gold miners with silicosis. Am J Respir Crit Care Med. 1994;150: Trapido, A.S., Mqoqi, N.P., Williams B.G., et al. Prevalence of occupational lung disease in a random sample of former mineworkers, Libode District, Eastern Cape Province, South Africa. Am J Ind Med. 1998;34: De la Hoz, R. Tuberculosis and silicosis. In: Rom W.N. & Garay, S. (eds). Tuberculosis: Little Brown and Company. Boston: New York, 1996; Murray J., Kielkowski, D. & Reid, P. Occupational disease trends in black South African gold miners. Am J Respir Crit Care Med. 1996;153: Kleinschmidt, I. & Churchyard, G. Variation in incidence of tuberculosis in subgroups of South African gold miners. Occup Environ Med. 1997;54: Steen, T.W., Gyi, K.M., White, N.W., et al. Prevalence of occupational lung disease among Botswana men formerly employed in the South African mining industry. Occup Environ Med. 1997;54: Hnizdo, E. & Murray, J. Risk of pulmonary tuberculosis relative to silicosis and exposure to silica dust in South African gold miners. Occup Environ Med. 1998;55: Schepers, S.W.H. Silicosis and tuberculosis. Ind Med & Surgery. 1964;33: International Labour Office. Guidelines for the use of the ILO International Classification of Radiographs of Pneumoconioses. Revised edition. ILO, Geneva, Ehrlich, R.I., Rees, D., Zwi, A.B. Silicosis in non-mining industry on the Witwatersrand. SAMJ. 1988;73: Classification of Pulmonary Tuberculosis. In: Diagnostic Standards and Classification of Tuberculosis: Chapter 6. New York: National Tuberculosis and Respiratory Disease Association, 1969; JULY/AUGUST