Miliary TB is characterised by lympho-hematogenous dissemination of MTB which results in the formation of tiny, discrete “millet seed-like” tubercules of granulomatous tissue in various organs of the body.
1,2 The diagnosis criteria of miliary TB relies on clinical findings consistent with TB such as fever, night sweats, loss of weight and appetite, and evening rise of temperature; along with microbiological/histopathological diagnosis of TB; and most importantly, the appearance of characteristic radiological findings on chest imaging.
2
Chest X-ray is the initial radiological investigation used to detect and diagnose miliary TB. The classical presentation of miliary TB is the appearance of miliary infiltrates on a radiograph.
2 These miliary opacities may be classified as typical (1-3 mm discrete nodules throughout the lung fields) or atypical (nodules larger than 3 mm or a reticulonodular miliary pattern).
3 However, this classic miliary pattern on chest X-ray is only seen in half the cases. In upto 30% cases, chest X-ray may show asymmetrical nodular lesions, coalescing nodules, mottled or snow-storm appearance, and lobar consolidation resembling typical or atypical pneumonias. In a small category of patients (about 5%), chest X-ray may even show segmental consolidation and pleural involvement (effusion, empyema, pneumothorax), as in our patient.
2
In addition to the variable radiographic appearance of miliary TB, due to the delayed appearance of miliary nodules or due to the presence of nodules below the threshold of perceptibility, initial chest X-ray may be normal.
1 The deposition of collagen and/or caseous material in the nodules is responsible for the appearance of miliary shadows on chest X-ray. This deposition is progressive and thus a typical miliary pattern may be delayed, evolving over the course of the disease.
2 Studies have found that the detection of miliary nodules radiologically may be delayed upto 2.5 weeks from the onset of fever.
3
CT chest is known to be more sensitive than X-rays for the identification of miliary opacities.
1 Choe et al.
4 found that initial CT chest missed the identification of miliary patterns in about 10% of the patients. In these 10% patients, classical miliary nodules appeared on the follow-up CT scan at a median duration of 29 days (range: 15-55 days). They found that ill-defined nodules and smaller-sized nodules less than 2 mm were independently and significantly associated with missed miliary TB.
4
Our patient had a past history of treated miliary TB and her initial X-ray did not show the classical miliary nodules. However, since she did not clinically respond to antibiotic therapy, suspecting a recurrence of miliary TB, we decided to repeat a chest X-ray for her. Her subsequent X-ray and chest CT showed characteristic miliary nodules. Thus, due to the delayed appearance of miliary opacities, if the disease is suspected, repeat chest imaging should be obtained.
| References : |
- Kim JY, Jeong YJ, Kim KI et al. Miliary tuberculosis: a comparison of CT findings in HIV-seropositive and HIV-seronegative patients. Br J Radiol. 2010 Mar;83(987):206-11.
- Sharma SK, Mohan A, Sharma A. Challenges in the diagnosis & treatment of miliary tuberculosis. Indian J Med Res. 2012 May;135(5):703-30.
- Mert A, Arslan F, Kuyucu T et al. Miliary tuberculosis: Epidemiological and clinical analysis of large-case series from moderate to low tuberculosis endemic Country. Medicine (Baltimore). 2017 Feb;96(5):e5875.
- Choe J, Jung KH, Park JH et al. Clinical and radiologic characteristics of radiologically missed miliary tuberculosis. Medicine (Baltimore). 2021 Feb 26;100(8):e23833.
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