SN7 SHORT NOTE 5M

Describe the forms of extrapulmonary tuberculosis with their diagnosis and treatment.

Microbiology · 2nd Professional — Para-Clinical

Overview

Extrapulmonary tuberculosis accounts for 15 to 20% of cases in immunocompetent patients, and a considerably higher proportion in HIV infection and in children
It is usually paucibacillary, which governs everything about its diagnosis — smears are usually negative, cultures are frequently negative, and the diagnosis often rests on histology, imaging, adenosine deaminase and a response to treatment
It is not infectious (except laryngeal disease and open sinuses), so isolation and contact tracing are generally unnecessary

Site	Features and diagnosis
Lymph node (the commonest)	Cervical nodes especially ("scrofula"); matted, may form a cold abscess and a discharging sinus. Diagnosis by fine needle aspiration for cytology, AFB and CBNAAT, or excision biopsy showing caseating granuloma
Pleural	An exudative effusion, lymphocyte-predominant, with a high adenosine deaminase and low glucose; pleural biopsy raises the yield considerably over fluid alone
Meningeal	The most lethal form. Insidious onset with fever, headache, vomiting and cranial nerve palsies (especially the sixth). CSF shows raised protein, low glucose, lymphocytosis and a cobweb clot; basal exudates and hydrocephalus on imaging. Treat ON suspicion — delay causes death and permanent disability
Spinal (POTT disease)	Usually thoracolumbar; destroys the vertebral bodies and intervertebral disc, producing a gibbus, cold (psoas) abscess and paraplegia. MRI is the investigation of choice
Abdominal	Ileocaecal disease mimicking CROHN disease and carcinoma; ascites with a high protein and high adenosine deaminase; "doughy" abdomen; adhesions and obstruction
Genitourinary	Sterile pyuria with acid urine is the classical clue; renal scarring, ureteric stricture and a contracted bladder. In women, tubal disease causing infertility — an important cause in India
Pericardial	Effusion progressing to constrictive pericarditis; steroids are given in addition to antitubercular treatment
Miliary	Haematogenous dissemination; "millet seed" mottling on chest radiograph, choroid tubercles on fundoscopy, and a frequently negative tuberculin test from anergy

CLINICAL PEARL

Tuberculous meningitis must be treated on suspicion, because waiting for proof costs the patient their neurological future. Cerebrospinal fluid microscopy is positive in only a small minority, culture takes weeks, and even CBNAAT is insensitive on this specimen. Outcome depends almost entirely on the stage at which treatment begins — patients treated while still fully conscious do well, and those treated after coma frequently die or survive disabled. The threshold for starting must therefore be low.

Diagnostic Approach

Obtain tissue or fluid wherever possible, and send it for histopathology, AFB smear, mycobacterial culture and CBNAAT — not for histology alone
CBNAAT is recommended as the initial test on extrapulmonary specimens, including cerebrospinal fluid, lymph node aspirate and pleural fluid, since it also reports rifampicin resistance
Adenosine deaminase is a cheap and useful supportive test in pleural, peritoneal and pericardial fluid and in cerebrospinal fluid, though it is not specific
Imaging — MRI for spinal and central nervous system disease, ultrasound and computed tomography for abdominal and nodal disease, and a chest radiograph in every case, which may show coexisting pulmonary disease
Search for concurrent pulmonary disease, which if present is easier to confirm bacteriologically and settles the diagnosis

Treatment and Applied Aspects

The same first-line drugs are used, with the intensive and continuation phases as in pulmonary disease; duration is extended to 9 to 12 months for meningeal, spinal and disseminated disease
Corticosteroids are indicated in tuberculous meningitis (where they reduce mortality) and in pericarditis; they reduce the inflammatory damage that is itself a large part of the pathology
Surgery for spinal instability or cord compression, hydrocephalus (shunting), intestinal obstruction, and constrictive pericarditis
Response is assessed clinically and radiologically, since there is no sputum to follow; paradoxical enlargement of nodes or lesions during treatment is common and does not by itself indicate failure
Test for HIV in every case, and particularly in disseminated or multi-site disease
Extrapulmonary tuberculosis is frequently diagnosed late in India because it is not suspected and because tissue is not obtained; the practical lesson is to biopsy early and to send the specimen for microbiology as well as histology

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