JULY/AUGUST 20034 OCCUPATIONAL HEALTH SOUTHERN AFRICA

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 identifi-

cation 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 co-

hort of 1153 gold miners for seven years and concluded

that of the 818 of these men with silicosis, one quar-

ter 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 radio-

logical 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 deter-

mining 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 radio-

graphic evidence of TB (see appendix on page 6).

The tubercle bacillus invades the respiratory tract

via the bronchial pathway. In the main the patho-

logical 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 pa-

thology, 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 clini-

cal 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 epidemio-

logical purposes, is paramount. Standardising

radiograph reporting in TB will enhance compara-

bility 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

Silicosis and tuberculosis

A proposed radiographic classification of tuberculosis to

accompany the ILO International Classification of Radio-

graphs of Pneumoconioses

ALBERT SOLOMON,PROFESSOR EMERITUS,

DAVID REES, MARIANNEFELIX, AND ENGELA

VENTER

OCCUPATIONALMEDICINE SECTION

NATIONAL CENTRE FOROCCUPATIONAL HEALTH

(NCOH)BOX 4788

JOHANNESBURG 2000TEL:011 712 6490

FAX: 011 720 5845 E-MAIL:

ventee@health.gov.za

Silicosis and concomitant tuberculosis: the rad iolo

PERMISSION TO

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THIS ARTICLE, WHICHORIGINALLY APPEAREDIN THE INTERNATIONAL

JOURNAL OF

OCCUPATIONAL AND

ENVIRONMENTAL

HEALTH 2000;6:215-219, ISREPUBLISHED WITH

KIND PERMISSION FROMTHE EDITOR, JOSEPH

LADOU. THEINTERNATIONAL

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5JULY/AUGUST 2003OCCUPATIONAL HEALTH SOUTHERN AFRICA

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 hospi-

tal 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 com-

mon. Nodular TB presents with a localised aggregation in a

much shorter time than silicotic nodules. A marked variabil-

ity 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 ex-

pected or more rapid progression of the radiographic changes.

In the region associated with this linear arraignment a promi-

nent hilar flare becomes evident.10 Unexpected supraclavicu-

lar 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 pulmo-

nary TB. Obvious pulmonary architectural distortion,

manifested by broncho-vascular-bundle and mediastinal dis-

tortion, fibrotic bronchiectasis, and volume loss, as well as

srad iologist’s enigma

JULY/AUGUST 20036 OCCUPATIONAL HEALTH SOUTHERN AFRICA

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 profu-

sion 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 opaci-

fication, bronchogenic dissemination and pleural and

pericardial involvement, usually offers little diagnostic diffi-

culty 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 ter-

minology, 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 report-

ing 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 infor-

mation 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 resi-

dence 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

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).

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 care-

ful review of standard 6 foot upright posteroanterior film, with

or without lateral projection. The interpreter’s grading is indi-

cated as an integer (0-3) or by writing the descriptive grade,

i.e. normal, minimal disease, moderately advanced.

Source: Classification of pulmonary tuberculosis. In: Diagnostic Standards and Classification of Tuberculosis. New York: National

Tuberculosis and Respiratory Disease Association, 1969;68-74.11

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

Grade no. Descriptive Grade Definition

Appendix:

7JULY/AUGUST 2003OCCUPATIONAL HEALTH SOUTHERN AFRICA

Extensive disease:

C cavity

P patchy opacification

S segmental (pneumonic/lobar)

BA broncho-alveolar (acinus

rosette)

M miliary

N nodal

Established lesions:

Nod nodules

Cic cicatrisation

FibBr 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 oblitera-

tion

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

TABLE I. GLOSSARY OF TERMS DESCRIBING THE TB LESIONS

contaminated, e.g. sand blasting or in uncontrolled mines.

Furthermore, initial radiographic changes are less preva-

lent 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 in-

dustry 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

• This conference offers you the knowledge,

understanding and guidelines to manage ethi-

cal issues in your work, whether it is in the

public or private sector, in the workplace or con-

sulting 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: 012 667 5160/1

e-mail: sasomdm@iafrica.com

SASOM ANNUAL CONFERENCE

Kopanong Conference Centre and Hotel,

Benoni

5 and 6 September 2003

Ethics in health

– a comprehensiveperspective

JULY/AUGUST 20038 OCCUPATIONAL HEALTH SOUTHERN AFRICA

FIGURE 1. TB X-RAY READING FORM

9JULY/AUGUST 2003OCCUPATIONAL HEALTH SOUTHERN AFRICA

REFERENCES

1. Cowie, R.L. The epidemiology of tuberculosis in gold

miners with silicosis. Am J Respir Crit Care Med.

1994;150:1460-1462.

2. 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;34:305-313.

3. De la Hoz, R. Tuberculosis and silicosis. In: Rom W.N. &

Garay, S. (eds). Tuberculosis: Little Brown and Company.

Boston: New York, 1996;525-530.

4. Murray J., Kielkowski, D. & Reid, P. Occupational disease

trends in black South African gold miners. Am J Respir Crit

Care Med. 1996;153:706-710.

5. Kleinschmidt, I. & Churchyard, G. Variation in incidence of

tuberculosis in subgroups of South African gold miners.

Occup Environ Med. 1997;54:636-641.

6. 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;54:19-26.

7. 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;55:496-502.

8. Schepers, S.W.H. Silicosis and tuberculosis. Ind Med &

Surgery. 1964;33:381-399.

9. International Labour Office. Guidelines for the use of the

ILO International Classification of Radiographs of Pneumoco-

nioses. Revised edition. ILO, Geneva, 1980.

10. Ehrlich, R.I., Rees, D., Zwi, A.B. Silicosis in non-mining

industry on the Witwatersrand. SAMJ. 1988;73:704-708.

11. Classification of Pulmonary Tuberculosis. In: Diagnostic

Standards and Classification of Tuberculosis: Chapter 6. New

York: National Tuberculosis and Respiratory Disease

Association, 1969;68-74.

reading sheet will have to be assessed, e.g. by the

radiographic assessment of workers with a post-

mortem 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 Inter-

national Labour Organisation classification.8 The

protocol for assessing the radiograph follows ILO in-

structions. Any radiographic change of a lesion

suspected to be TB would call for the additional reading

classification. In the case of widely disseminated bron-

chogenic 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 rec-

ognised 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 prob-

lem of control.