Description

A man in his 40s presented with low-grade fever, weight loss and intermittent cough with scanty sputum for a duration of 1 month. There was no history of smoking, occupational exposure or any immunocompromised conditions. On examination, there were few scattered crepitations present on chest auscultation, while other systemic examinations were within normal limit. All blood parameters were also normal except mild elevation in erythrocytic sedimentation rate. A chest radiograph showed numerous micronodular opacities in both lung fields (figure 1). Subsequently, a high-resolution CT scan of chest confirmed the presence of multiple micronodules in both lung fields in a random distribution (figure 2). No focal lung lesion or mediastinal lymphadenopathy was noted. Induced sputum using hypertonic saline showed acid-fast bacilli on Ziehl-Neelsen stain. Sputum workup for bacterial and fungal infections (stains and culture) was negative. With a diagnosis of miliary tuberculosis, the patient was started on first-line antitubercular drugs.

• Download figure
• Open in new tab
• Download powerpoint

Figure 1

Chest radiograph showing multiple small nodules (red arrowhead), distributed throughout both lung fields.

• Download figure
• Open in new tab
• Download powerpoint

Figure 2

Axial CT images of thorax, showing multiple miliary nodule (red arrow) of size 1–4 mm (measuring Hounsfield Units +430) randomly distributed in both lung fields.

A miliary pattern on chest radiology is described as multiple small pulmonary nodules measuring <2–3 mm, randomly distributed in bilateral lung fields.1 The miliary nodules in CT chest correspond approximately to size of millet seeds (Pennisetum typhoides, bajra) and hence the term ‘miliary’ was used. Although classically associated and described in miliary tuberculosis, this pattern is also seen in other infectious as well as non-infectious aetiology. Miliary tuberculosis usually results from lymphohematogenous dissemination of tubercular bacilli to vascular bed of various organs including lungs and is commonly seen in children, elderly and immunocompromised individuals.2 Diagnosis of miliary tuberculosis is based on clinical features consistent of tuberculosis (fever, night sweats, anorexia and weight loss), with typical miliary pattern on chest radiograph or CT chest plus microbiological and/or histopathological evidence of tuberculosis.2 Other organ systems may also be involved in miliary tuberculosis like neurological (meningitis with or without tuberculoma), ophthalmic (choroidal tubercles), dermatological (tuberculosis miliaria cutis), hepatosplenic system, etc.3 The nodules usually resolve within 2–6 months with antitubercular treatment, without scarring or calcification. Other infectious disease, where miliary pattern is seen includes disseminated fungal infections like blastomycosis, cryptococcosis, histoplasmosis or coccidioidomycosis. Diagnosis only based on imaging is difficult and other ancillary tests like bronchoscopy with transbronchial biopsy, serology antibody and antigen testing are paramount in clinching the diagnosis.4 Miliary pattern is also seen in primary lung malignancy or metastasis from highly vascular tumour like renal cell carcinoma and melanoma or from breast, thyroid and prostate neoplasms.5 Non-small cell lung cancer with epidermal growth factor receptor mutations have high propensity for miliary lung metastasis.6 Other uncommon aetiologies mimicking miliary pattern includes sarcoidosis, pneumoconiosis (silicosis), hypersensivity pneumonitis or rarely pulmonary alveolar microlithiasis.7 Although pulmonary tuberculosis commonly presents with radiological features like consolidation, cavity, nodules,8 etc, it can on rare occasions present with uncommon manifestations.9 10 Miliary mottling on chest imaging is a relatively uncommon manifestation of pulmonary tuberculosis (seen in <2% of tuberculosis in immunocompetent persons), which should be kept as a strong differential in appropriate clinical setting.