Right lung miliary tuberculosis - Erler Zimmer
Clinical History
A 74-year-old male presented with worsening shortness of breath, haemoptysis, 20kg weight loss over 6 months, night sweats, and a chronic cough. Having recently moved from a country where TB is endemic, he exhibited hypoxia, tachypnea, bilateral crepitations throughout his lung fields, and a dull left lung base on percussion. His positive quantiferon gold blood test and chest x-ray revealing bilateral small nodular deposits and left basal pneumonia led to a diagnosis of miliary tuberculosis. Unfortunately, he succumbed to respiratory failure shortly after admission.
Pathology
The right lung, sliced longitudinally, displays mildly ectatic bronchi and bronchioles. Throughout the lung parenchyma, numerous small pale yellow nodules, measuring less than 1 mm in diameter, are scattered. Similar tiny subpleural nodules are evident on the surface of the visceral pleura. These nodules are tubercles, indicative of miliary tuberculosis, named for their resemblance to millet seeds.
Further Information
Tuberculosis (TB), caused by Mycobacterium tuberculosis, is a chronic pulmonary and systemic infectious disease. Transmission typically occurs through inhalation of aerosolized droplets. Risk factors include residence in developing countries where TB is endemic, immunosuppression (e.g. HIV, steroid use, anti-TNF use, and diabetes), chronic lung disease (e.g. silicosis), alcoholism, and malnutrition.
Following initial pulmonary infection, individuals may enter an asymptomatic latent infection phase. In 90% of cases with an intact immune system, latent TB may later reactivate. The remaining 10%, especially the immunocompromised, develop immediate active TB infection with manifestations ranging from pulmonary symptoms to extra-pulmonary involvement, including lymphadenopathy, meningitis, and disseminated miliary TB.
Reactivation of latent TB, termed secondary tuberculosis, occurs in around 10% of cases during periods of weakened host immunity. Symptoms include cough, haemoptysis, fever, night sweats, and weight loss.
Miliary TB arises when mycobacteria erode into a pulmonary vein and disseminate, circulating through the arterial system, commonly depositing in the liver, bone marrow, spleen, and adrenal glands. The immune response involves TH1 cells stimulating alveolar macrophages to form granulomas surrounding central areas of 'caseous' necrosis.
Diagnosis involves clinical history, chest x-ray, multiple sputum cultures, Mantoux skin tuberculin test, and serum interferon gamma release assay. Biopsies may be taken for culture. Treatment requires prolonged courses of multiple antibiotics based on mycobacterial resistance.
