Miliary Tuberculosis

Definition: In predisposed, immunocompromised individuals, miliary disease develops when many organisms simultaneously gain access to pulmonary or systemic veins. Lesions all of the same age, 1-3 mm in diameter, appear in many organs throughout the body.

 

CT appearance: CT shows multiple, small (1-3 mm) nodules that are randomly positioned in the parenchyma, and along the pleura and fissures. They are especially well seen in the right upper lobe. This random pattern is the CT equivalent of a miliary pattern and is distinguished from a pure centrilobular pattern by nodules seen at the pleural surfaces and at the ends of vessels. The nodules appear randomly, rather than uniformly, spaced, as in centrilobular nodules (see diagram).

What is the differential diagnosis of miliary nodules in the lung? Answer

 

Gross appearance: The slice of lung (left panel) shows multiple grey spots corresponding to granulomas all at the same stage of development. The millet seeds (right), for which the pattern is named, have a similar size.

Histologic appearance: The granulomas are usually less well-defined than in immunocompetent hosts. Note the poorly-formed epithelioid cells with little visible cytoplasm. The arrow indicates a multinucleated giant cell. There are many lymphocytes scattered throughout.

Miliary Tuberculosis

Miliary tuberculosis is a severe form of disease with a high mortality rate. A recent retrospective study of seven patients with miliary disease and six patients with tuberculous pneumonia, all of whom required mechanical ventilation, defined pneumonia as parenchymal disease other than miliary. Miliary disease (as shown above) included disseminated multiorgan disease. Risk factors for both included ethanol abuse and malnourishment. Acute respiratory distress syndrome (ARDS) occurred in 10 of the13, and stays in the intensive care unit and total hospital days were prolonged (mean 19 da and 50 da, respectively). The hospital mortality rate was 69% compared with the rate for non-tuberculous pneumonia patients requiring mechanical ventilation of 36% (p <0.025). However, the hospital mortality rate for those who developed ARDS (69%) was similar to that of patients with other pneumonias who developed ARDS (56%).

In the Canadian province where the study was performed, the incidence of miliary tuberculosis requiring mechanical ventilation was 20 times greater than that of tuberculous pneumonia requiring ventilation. This predisposition of miliary disease to respiratory failure and ARDS was attributed to the diffuse spread of organisms. One of the cell wall components of the bacillus, lipoarabinomannan, like lipopolysaccharide of non-tuberculous ARDS, causes macrophages to release inflammatory cytokines, TNF-alfa and IL-1 beta, which may precipitate acute lung injury [1].

Reference:

1. Penner C, Roberts D, Kunimoto D, Manfreda J, Long R. Tuberculosis as a primary cause of respiratory failure requiring mechanical ventilation. Am J Respir Crit Care Med 1995; 151:867-872.

Clinical summary Other manifestations of tuberculosisDiscussion

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Answer: Miliary nodules usually result from hematogenous spread of disease including TB, fungi, metastatic tumor (especially thyroid and renal), and intravascular spread of intravesical BCG. A miliary pattern has also been seen with bronchioloalveolar carcinoma and sarcoidosis.