- Tuberculosis is common throughout the world
- Causes significant morbidity and mortality particularly in Africa and Asia
- Over 10,000 cases per year occur in United Kingdom
- Accounts for 1,000 deaths mainly in immigrant Asian population
- Usually due to Mycobacterium tuberculosis or Mycobacterium bovis infection
Primary tuberculosis
- Usually a respiratory infection that occurs in childhood
- Infection results in sub-pleural Ghon focus and mediastinal lymphadenopathy
- Regarded as the primary complex
- Symptoms are often few
- Resolution of infection usually occurs
- Complications include:
- Haematogenous spread causing miliary TB affecting lungs, bones, joints, meninges
- Direct pulmonary spread resulting in TB bronchopneumonia
Post-primary tuberculosis
- Occurs in adolescence or adult life
- Due to reactivation of infection or repeat exposure
- Results in more significant symptoms
- Reactivation may be associated with immunosuppression (e.g. drugs or HIV infection)
- Pulmonary infection accounts for 70% of cases of post-primary TB
- Usually affects apices of upper or lower lobes
- Cavitation of infection into the bronchial tree results in 'open' TB
- Clinical features include cough, haemoptysis, malaise, weight loss and night sweats
- Infection of lymph glands results in discrete, firm and painless lymphadenopathy
- Confluence of infected glands can result in a 'cold' abscess
- Infection of the urinary tract can cause haematuria and 'sterile pyuria'
Investigations
Microscopy
- If Mycobacteria infection suspected samples should be submitted to a Ziehl-Neelsen stain
- Mycobacteria appear as red acid-alcohol fast organisms
- Organisms also fluoresce with auramine staining
- Negative microscopy does not exclude tuberculosis
- Need supporting histological examination and microbiological culture
Culture
- Mycobacteria can be difficult to culture
- Need to:
- Collect adequate and relevant specimens (e.g. early morning urine x3)
- Concentration of specimen (e.g. centrifugation)
- Decontamination to remove other organisms (e.g. Petroff method)
- Culture on Lowenstein-Jensen method at 35-37°
for at least 6 weeks
- Confirm that any Mycobacteria cultures are pathological
Histology
- Histological examination shows evidence of a delayed hypersensitivity reaction
- Classical appearance is of caeseating necrosis
- Tuberculosis follicle consists of central caseaous necrosis
- Surrounded by lymphocytes, multi-nucleate giant cells and epitheloid macrophages
- Organisms may be identified within the macrophages
Picture provided by Neha Dohuya, KG Hospital, Coimbature, India
Skin tests
- Delayed hypersensitivity reaction used to diagnose tuberculosis
- The two commonest tests are the Mantoux and Heaf test
- In the Mantoux test 0.1 ml of purified protein derivative is injected intradermally
- Positive reaction is a papule of > 5 mm diameter at 72 hours
- In the Heaf test purified protein derivative is placed on the skin
- A gun is used to produce multiple punctures
- Positive reaction is more than 4 papules at puncture sites at 72 hours
- Positive skin test are indicative of active infection or previous BCG vaccination
Treatment
- First line chemotherapeutic agents are rifampicin, isoniazid and ethambutol
- Given as 'triple therapy' for first 2 months until sensitivities available
- Rifampicin and isoniazid are the usually continued for further 7 months
- Less than 5% of organisms are resistant to first-line agents
- Second line treatment includes pyrazinamide
Bibliography
Aston N O. Abdominal tuberculosis.
World J Surg 1997; 21:
492-499
Carl P, Stark L. Indications
for the surgical management of genitourinary tuberculosis. World
J Surg 1997; 21: 505-510.
Kapoor V K. Abdominal tuberculosis.
Postgrad Med J 1998; 74:
459-467. |