Tissue and bone infection: TB

Question 1

How is TB in bones and joints classified?

Answer 1

• Extra-articular - outside the joint - epiphyseal/bone with haemodynamic marrow
• Intra-articular - inside the joint - large joints - knee
• Vertebral body

Question 2

True or false: 2/3 of patients have tb in only 1 site

Answer 2

True

Question 3

Clinical features of TB infection in bone/joints

Answer 3

• Insidious onset + general decline in health
• Contact with TB
• Pain (esp. at night), swelling, loss of weight (often confused with bone tumour)
• Low grade pyrexia
• Joint swelling - decrease ROM ankylosis – failure to move the joint
• Deformity

Question 4

Pathology of the TB infection

Answer 4

1. Primary complex occurs in the lung or the gut
2. Secondary spread to site
3. TB granuloma at the site (bone or joint)

Question 5

TB found in the spine is becoming more common.

How does it present?

Answer 5

• Little pain
• Cold abscess
• Severe kyphosis due to vertebral collapse

Question 6

What is meant by a ‘cold abscess’?

Answer 6

Cold abscess refers to an abscess that lacks the intense inflammation usually associated with infection. TB infection does not tend to stimulate acute inflammation.

Question 7

What might you expect to see when making a diagnosis of TB? (4)

Answer 7

• Often a long history
• Involvement of single joint makes diagnosis of TB more likely
• Marked thickening of the synovium
• Marked muscle wasting peri-articular osteoporosis – bone around the joint becomes osteoporotic - more susceptible to fractures etc

Question 8

Which investigations are done to diagnose TB?

Answer 8

• FBC, ESR
• Mantoux test
• Interferon gamma release assay
• Sputum/urine culture
• X-ray (CXR and limbs) - soft tissue swelling, periarticular osteopaenia (bone thinning which is an indication of past inflammation around a certain joint), articular space narrowing
• Joint aspiration and biopsy

Question 9

Differential diagnoses?

Answer 9

• Transient synovitis
• Monoarticular RA
• Haemorrhagic arthritis
• Pyogenic arthritis - v common

Question 10

Treatment of TB

Answer 10

Chemotherapy

Initially for 3 months:

• Rifampicin and Isoniazid
• Ethambutol

Then for 6-12 months

• Isoniazid

Rest and splintage

Question 11

Common side effects of TB drugs

Answer 11

• Isoniazid - peripheral neuropathy ‘I-so-numb-azid’
• Rifampicin - orange/red urine or tears ‘red-an-orange-pissin’
• Ethambutol - colour blindness / altered visual acuity ‘eye-thambutol’