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How not to miss pulmonary tuberculosis

Consultant physician and TB specialist Professor Peter Davies explains the signs, symptoms and key questions to ask if you suspect TB

Consultant physician and TB specialist Professor Peter Davies explains the signs, symptoms and key questions to ask if you suspect TB

Worst outcomes if missed

• Death

• Destruction of lung with resultant severe breathlessness

• Fibrosis and bronchiectasis, which may cause chronic respiratory infections in future

• Spread of disease to contacts by airborne transmission

• Speed of diagnosis and starting treatment will reduce incidence of complications

Epidemiology

Tuberculosis cases have been steadily rising in the UK from a low of about 5,000 in 1987 to more than 8,200 in 2006. This is mainly because of people going to and returning from high-burden countries.

Screening should take place at port of entry and first residence. Screening for active disease is relatively straightforward but screening for latent infection is more problematic.

TB is most common in developing nations, particularly those with high HIV prevalence.

Incidence of TB in the African-born population is 100 times that of the UK-born white population. Incidence in the Indian-born population is 20 times greater.

Other risk factors include other causes of immunosupression, diabetes, gastrectomy, malignancy, smoking, drug abuse and homelessness.

Symptoms and signs

• Chronic cough productive of phlegm and sometimes blood.

• Malaise.

• Weight loss, which may be marked, reaching up to 25% of body mass before presentation.

• Night sweats.

• Sometimes chest pain.

• Breathlessness, in advanced disease.

• Speed of onset is slow and patients may be ill for two to three months before presenting.

• In advanced cases, signs of pneumonia with reduced breath sounds and crackles may be present over the affected part of the lung, usually the upper lobes.

• If total lobe destruction has occurred, amphoric breathing (the noise made by blowing over the top of an empty bottle) may be heard.

• Chest X-ray changes are usually much more extensive than chest physical signs would suggest.

• Presentation in children may be less marked; history of contact with infected adult usually present.

Diagnosis

41210632Chest X-ray provides a non-specific diagnosis. Characteristic features are soft ‘fluffy' shadows with cavitation predominantly in upper lobes but immunomodulation, particularly with HIV co-infection, can result in virtually any pattern of abnormality.

Sputum specimens sent for staining for acid-fast bacilli and culture provide the specific diagnosis. Tuberculosis is confirmed by the culture of the bacteria from a specimen.

The tuberculin skin test (Mantoux) is usually positive but may be negative if disease is severe or another cause of immunodeficiency is present. A positive test indicates infection, but not necessarily disease.

BCG is the most common cause of a falsely negative test.

The new gamma interferon release assay tests are more sensitive and specific than the skin test but should only be used after a positive tuberculin skin test. Like the skin test, a positive test indicates infection, not necessarily disease.

Differential diagnosis

• Lung cancer in the older patient. Chronic cough with haemoptysis and weight loss mimic TB and vice versa.

• Asthma in the younger patient. Can be a cause of chronic cough but weight loss is unusual.

• Other pneumonic lung infection. Symptoms tend to be much more acute – well to severely ill in hours and days rather than weeks and months.

• Sarcoidosis. Does not usually cause serious malaise and weight loss but may do. The chest X-ray of stage 3 sarcoid can look very like tuberculosis.

• Lymphoma. Mediastinal gland enlargement may mimic primary tuberculosis, normally seen in children.

Professor Peter Davies is a consultant physician at the Liverpool Heart and Chest hospital and Aintree University Hospital

Competing interests: Professor Davies has acted as adviser to Oxford Immunotech and Genus Pharma

Further reading


NICE guideline on tuberculosis

Five red herrings

Five red herrings

• Chronic cough and weight loss in an older white smoker with an abnormal chest X-ray is more likely to be lung cancer than tuberculosis.
• In the older white patient, a positive sputum smear for acid fast bacilli is more likely to be caused by environmental mycobacteria (atypical) than M. tuberculosis. A PCR and gene probe test for M. tuberculosis can exclude the diagnosis of tuberculosis in these patients with 95% accuracy.
• Night sweats may also be caused by malignancy, especially lymphoma.
• There are many other causes of upper zone chest X-ray abnormalities; other infections and bronco-pulmonary aspergillosis in the asthmatic are common mimickers.
• The most common serious cause of malaise and pyrexia in a traveller to high-prevalence country is malaria.

key questions TB showing in upper left lung on X-ray TB showing in upper left lung on X-ray

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