Silicosis in TB Patients

Silicosis is a progressive and disabling interstitial lung disease caused by inhalation and deposition in the lungs of particles of free silica.

Mutual Risk of TB and Silicosis

• TB is a clinical complication of silicosis, called silico-tuberculosis. Silica-exposed workers with or without silicosis are at increased risk for TB. There is also an increased risk of extrapulmonary TB in individuals exposed to silica.
• The risk of a patient with silicosis developing TB is 2.8 – 3.9 times higher than a healthy individual.
• The risk of TB relapse in patients with silicosis is approximately 1.5 times higher than in patients without silicosis.

The presence of silica particles in the lung and silicosis may:

• Facilitate initiation of TB infection and progression to active TB
• Exacerbate the course and outcome of TB, including prognosis and survival

Diagnosis

The diagnosis of silicosis is made based on a history of exposure to silica accompanied by a clinical and radiological profile consistent with the disease.

Under the Integrated Management Algorithm for TB disease and TB infection released by the National TB Elimination Programme (NTEP), patients with silicosis are first screened according to the four-symptom complex to rule out/in active TB and tested for TB accordingly. 

If active TB is ruled out >> Refer for Tuberculin Skin Test (TST)/ Interferon Gamma Release Assay (IGRA) >> Positive test >> Evaluate with Chest X-ray (CXR) >> Commence TB Preventive Therapy (TPT) irrespective of CXR results.

CXR often indicates TB in silicosis patients earlier than the clinical symptoms, and regular radiographic screening is required for early TB detection. Radiographic comparison of serial films is done with particular attention to:

• Rapid appearance of new opacities, symmetric nodules or consolidation and the finding of pleural effusion or excavations.
• Cavitation is the strongest indicator of probable silico-tuberculosis.

Other diagnostic tools that can help in diagnosis are:

• Chest Computed Tomography (CT) scan
• Bronchoscopy with bronchoalveolar lavage in conjunction with transbronchial biopsy
• Spirometry

Treatment and Follow-up

To keep the disease from getting worse, all silicosis patients need to eliminate any more exposure to silica. Supportive measures include the use of cough medicines, bronchodilators, oxygen therapy and pulmonary rehabilitation.

TB treatment in patients with silicosis is challenging, perhaps due to impairment of macrophage function by free silica and/or poor drug penetration into fibrotic nodules. Usual anti-TB drugs with directly observed therapy are recommended but for an extended duration of at least 8 months, to reduce the chances of relapse.

Follow-up of patients with silicosis and TB follow the same schedule as is in prevailing guidelines.

Prevention

TB prevention in silicosis patients is essential and includes:

• Active surveillance of vulnerable groups including workers
• Adoption of measures to reduce exposure to silica dust
• Patients with silicosis are eligible for TPT after ruling out active TB

NTEP is in the process of engaging with the Ministry of Labour and Mining to identify high priority districts with stone crushing units/ mining industry. Specific guidelines will be developed to support persons with an occupational risk for TB and provide access, diagnosis and treatment services from the programme.

Resources

• NTEP at a Glance; Comprehensive Clinical Management Protocol of Tuberculosis, 2022.
• Training Modules (1-4) for Programme Managers and Medical Officers, 2020.
• Silico-tuberculosis, Silicosis and Other Respiratory Morbidities Among Sandstone Mine-workers in Rajasthan - A Cross-sectional Study, Saranya Rajavel et al., 2020.
• Mini-review: Silico-tuberculosis; Massimiliano Lanzafame et al, 2021.
• Immunity to the Dual Threat of Silica Exposure and Mycobacterium tuberculosis, Petr Konečný et al., 2019.

Assessment

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