Silicosis and tuberculosis - Occupational Health Source: Classification of pulmonary tuberculosis....
Transcript of Silicosis and tuberculosis - Occupational Health Source: Classification of pulmonary tuberculosis....
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:
Silicosis and concomitant tuberculosis: the rad iolo
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THIS ARTICLE, WHICHORIGINALLY APPEAREDIN THE INTERNATIONAL
JOURNAL OF
OCCUPATIONAL AND
ENVIRONMENTAL
HEALTH 2000;6:215-219, ISREPUBLISHED WITH
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OCCUPATIONAL AND
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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
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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:
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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
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Ethics in health
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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.