September
Definition
Chronic infection caused by Mycobacterium tuberculosis.
Epidemiology More common in Asians, immuno-compromised, homeless. 500 times more common in patients with HIV. The incidence doubled in the US between 1987 and 1991. Rates are higher in urban areas. Only around 5-10% of patients with TB have bone or joint involvement.
Etiology
Musculoskeletal disease is usually secondary to primary disease in the lungs or GIT.
Pathology
The disease affects joints more commonly than bones. Spinal involvement is most common. The hip is next most commonly affected. The primary complex is the site of initial infection plus its draining lymph nodes – often the lung, or the gut. TB is able to survive for years in the draining nodes. Secondary systemic spread occurs if there is low resistance to the primary complex, resulting in miliary TB. The bony lesions are tertiary or reactivated lesions. The characteristic appearance is of a central area of caseous necrosis surrounded by multinucleated giant cells (epithelioid cells) and lymphocytes. If the synovium is involved it becomes thick and oedematous and gives rise to a marked effusion. A pannus of granulation tissue may spread across the joint and destroy the cartilage. Increased vascularity leads to localized osteoporosis.
Clinical features
The onset is usually insidious. There may be a history of exposure to TB or prior infection. The patient may present with pain, swelling and muscle wasting, or with constitutional features such as fever and weight loss. The affected joint may be markedly swollen Spinal pathology may present with an acute kyphosis (gibbus) or a cold abscess pointing in the groin.
Radiology
The initial findings are rarefaction, followed by bone destruction and joint narrowing. There is a marked absence of sclerosis and periosteal reaction. The growth plate is not a barrier to infection. Caseous material may calcify late, which is characteristic of the infection. MRI scans typically show large intra-articular effusions, and gross thickening of the synovial membrane.
Investigations
Positive Mantoux test if the patient isn’t anergic. Synovial biopsy and culture will be positive in up to 80%. The WCC and ESR are mildly raised; if the ESR is greater than 50 this suggests a pyogenic infection.
Differential diagnosis
Rheumatoid arthritis Brucellosis – found in patients who drink unpasteurized milk, causes chronic granulomatous infection, treated with tetracycline.
Management
Rest
Chemotherapy
The standard drugs are rifampicin and isoniazid, used for 9 months. Pyrazinamide is used for the first 2 months. Ethambutol may be added but is associated with retrobulbar neuritis. Streptomycin is rarely used because of problems with nephro and ototoxicity. Surgery may be required to drain pus, remove necrotic bone, correct deformity or perform an arthrodesis.
Preantibiotic natural history of tuberculosis The average time spent in hospital prior to antibiotics was incredible: Knee 2 years
Hip 3 years
Spine 5 years
It was not considered safe to operate on patients with TB until the ESR had fallen, because if operated on prior to this there was a significant risk of causing miliary TB which was often fatal. The mainstays of treatment were bed rest for the patient, splintage for the limb and good food and fresh air.
Unusual presentations of tuberculosis
Tuberculous dactylitis (aka spina ventosa)
Occurs in the short tubular bones of the hands and feet. Most common in children (particularly under 5). Usually multiple lesions, of consecutive rather than simultaneous onset. On XR typical appearance is diffuse soft tissue swelling, bone expansion, thinning of the cortex. Associated joint disease is very rare. Spina ventosa means: spina- thornlike and ventosa- inflated with air Saw XR presented by Dr Chapman at RNSH July 99.
Mycobacterium marinum
This causes chronic skin infections, and is sustained after a skin breach often in swimming pools or while fishing. This atypical mycobacterium needs to be cultured at 30 degrees celcius.
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