Definition- Miliary TB is defined as millet like (mean 2 mm, range 1-5 mm) seeding of TB bacilli in the lung, as evidenced on chest radiography. This pattern is seen in 1-3% of all TB cases.
Miliary TB may occur in an individual organ (very rare, <5%), in several organs, or throughout the whole body (>90%), including the brain.
The infection is characterized by a large amount of TB bacilli, although it may easily be missed and is fatal if untreated.
Pathophysiology-
Following exposure and inhalation of TB bacilli in the lung, a primary pulmonary complex is established and pulmonary lymphangitis and hilar lymphadenopathy develop.
Mycobacteremia and hematogenous seeding occur after the primary infection. After initial inhalation of TB bacilli, miliary TB may occur as primary TB or may develop years after the initial infection. Radio graphically, they are not calcified (as opposed to the initial Ghon focus, which often is visible on chest radiographs as a small calcified nodule.
Mortality-
1) Untreated, the mortality rate is assumed to be close to 100%. With early and appropriate treatment, the mortality rate is reduced to less than 10%.
2) Most deaths occur within the first 2 weeks of admission to the hospital. This may be related to delayed onset of treatment.
3) Up to 50% of all cases of disseminated TB detected at autopsy were missed ante mortem in reported case series
Age-
1) Children younger than 5 years who acquire miliary TB are more likely to develop life-threatening miliary and/or meningeal TB.
2) Adults older than 65 years have a higher risk of miliary TB.
Symptoms-H/o weakness, fatigue (90%) ,headache(10%),weight loss(80%).
Signs-
1) Low grade fever(80%)
2) Cough (60%)
3) Lymphadenopathy (40%)
4) Hepatosplenomegaly (40%)
5) Pancreatitis (10%)
6) Multiorgan dysfunction.
Causes-
Risks factor involve in immunosupression-
1)HIV
2)cancer
3)Transplatation.
4)Malnutrition.
5)Diabetes
6) Silicosis.
7) End stage renal disease.
Differential diagnosis-
1)Acute Respiratory Distress Syndrome
2)Addison Disease
3)Blasto mycosis
4)Bone Marrow Failure
5)Cardiac Tamponade
6)Disseminated Intravascular Coagulation
7)Eosinophilic Pneumonia
8)Epididymal Tuberculosis
9)Histoplasmosis
10)Hypersensitivity Pneumonitis
11)Pneumocystis Carinii Pneumonia
12)Pneumonia, Bacterial
13) Pneumonia, Fungal
14)Pneumonia, Viral
15)Sarcoidosis
16)Silicosis
17) Histiocytosis X (Langerhans cell histiocytosis) .
18) HIV-related pulmonary opportunistic infections.
1)Acute Respiratory Distress Syndrome
2)Addison Disease
3)Blasto mycosis
4)Bone Marrow Failure
5)Cardiac Tamponade
6)Disseminated Intravascular Coagulation
7)Eosinophilic Pneumonia
8)Epididymal Tuberculosis
9)Histoplasmosis
10)Hypersensitivity Pneumonitis
11)Pneumocystis Carinii Pneumonia
12)Pneumonia, Bacterial
13) Pneumonia, Fungal
14)Pneumonia, Viral
15)Sarcoidosis
16)Silicosis
17) Histiocytosis X (Langerhans cell histiocytosis) .
18) HIV-related pulmonary opportunistic infections.
Lab diagnosis-
1) CBC- leucopenia/leucocytosis,Anemia, Thrombocytopenia, rarely thrombocytosis.
2) ESR raised-50% cases
3) Cultures- for mycobacterium (sputum, blood, urine, cerebral spinal fluid [CSF], and other body fluids.
Imaging study-
1) Chest radiography-
- Findings are typical in 50% of cases.
- A bright spotlight helps to reveal miliary nodules.
- Bilateral pleural effusions indicate dissemination versus localized and unilateral pleural TB. This may be a useful clinical clue.
- Nodules characteristic of miliary TB may be better visualized on lateral chest radiography (especially in the retro cardiac space).
2) HRCT finding in Miliary tuberculosis-
1) It shows very fine nodular or reticulonodular pattern on HRCT.
2) Majority nodules measures 1-3 mm diameter but some 5mm in diameter.
3) Nodules distributed randomly with out cephalocaudal, central to peripheral or interlobular predominance.
4) Nodules also present in sub pleural and perivascular region.
5) Miliary nodules can be distinguished from nodules seen in association with endobronchial spread because of their smaller size, uniform diameter, even distribution through out the lung and because they are unassociated with evidence of bronchial wall thicking.
HRCT finding in active tuberculosis-
1) Patchy unilateral or bilateral airspace consolidation frequently peribronchial in distribution.
2) Cavitations - thin or thick walled.
3) Scattered air space nodules, centrilobular branching structure, TREE IN BUD.
4) Superimposition of first three finding.
5) Miliary – small well defined nodules.
6) Pleural effusion, bronchopleural fistula, empyema necessitatis.
7) Low density mediastial /hilar lymph nodes.