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Chapter 3: Respiratory infections 105

features are fever (drenching night sweats are rare) be normal, as tubercles are not visible until they are
and cough productive of mucoid, purulent or blood 1–2 mm.
stained sputum. A pleural effusion or pneumonia TB can mimic almost any disease, radiographically,
may be the presenting sign, chest signs are often so confirmation of the diagnosis must be by stain-
absent and finger clubbing is only evident in late ing and culture of material such as sputum, early
disease. morning urine samples, cerebrospinal fluid, broncho-
3 Miliary tuberculosis may present in a non-specific scopic washings, pleural, transbronchial, lymph node,
manner with vague ill health, weight loss and fever. or bone marrow solid organ biopsy.
As dissemination progresses there may be tubercu- Microscopy with Ziehl–Nielsen staining or auramine
lous meningitis, choroidal tubercles seen in the eye fluorescent stain for acid fast bacilli (AFB). Rapid re-
and hepatosplenomegaly. sults can be obtained with polymerase chain reaction
(PCR) and DNA probes, which are highly sensitive;
however, they may be positive with no active disease.
Microscopy
Formal culture of material is the only way of accu-
The characteristic lesion, the tubercle (granuloma) con-
rately determining virulence and antibiotic sensitivity
sists of a central area of caseous tissue necrosis within
and should be attempted in every case, results may
which are viable mycobacteria. This central area is sur-
take 4–6 weeks.
rounded by a layer of activated macrophages and oc-
HIV testing should be performed in all patients diag-
casional multinucleate macrophages (Langerhans’ giant
nosed with TB, even those without known risk factors,
cells). Around the macrophage zone is a collar of lym-
as patients with HIV are much more likely to have sys-
phocytes and an outer coating of fibroblasts.
temic organ involvement, relapse after treatment and
may need lifelong treatment with isoniazid to prevent
Complications reactivation. They will also benefit from HIV specific
Fungal infection of cavitated areas of old TB infection treatment to improve their immune response.

forming a mycetoma. Tuberculintestingisusedforcontacttracingandprior
An enlarged lymph node may compress a bronchus,

to vaccination, it is used to assess exposure and sensiti-
causing collapse of a segment or lobe of the lung. This
sation to TB. It relies on the hypersensitivity reaction,
usually heals spontaneously but occasionally may per-
and is rarely helpful in the diagnosis of tuberculosis:
sist giving rise to bronchiectasis particularly of the
i The Tine test and Heaf test are for screening: 4/6
middle lobe (Brock’s Syndrome).
point needles coated with old tuberculin are used to
Metastatic TB: Bone marrow invasion may lead to a

puncture the skin, 72 hours after the test a hypersen-
pancytopenia. Bone involvement may lead to patho-
sitivity reaction is present. If the spots are confluent,
logicalfractures,particularlyofthespinetogetherwith
the test is positive, indicating exposure. In an im-
a paravertebral abscess. Tuberculous meningitis, tu-
munised adult no TB treatment is required as long
berculous peritonitis or tuberculous pericarditis may
as there is no evidence of infection.
occur.
ii The Mantoux test involves injecting a purified pro-
tein derivative intra dermally. The reaction is read at
Investigations 48–72 hours and is said to be positive if the indura-
An abnormal chest X-ray is often found incidentally tion is 10 mm or more in diameter, negative if less

in the absence of symptoms, but it is very rare for a than 5 mm.
case of pulmonary tuberculosis to be present if the If the test is positive with a low concentration of
chest X-ray is completely normal. The X-ray shows purified protein derivative this can indicate active
patchy or nodular shadowing in the upper zone with infection requiring treatment. In an immunocom-
fibrosis and loss of volume; calcification and cavita- promised host (such as chronic renal failure, lym-
tion may also be present. There may be calcification in phoma or HIV) or patients with miliary TB, the tests
the pericardial sac. In miliary TB the chest X-ray may may be falsely negative.