Pott's disease

History

• Percivall Pott published his account of lower-limb palsy with spinal deformity in 1779, and the eponym was applied to the tuberculous form once its infective nature was established.
• Robert Koch identified Mycobacterium tuberculosis in 1882, which separated tuberculous spondylitis from the other destructive spinal diseases grouped under the older term caries.
• Streptomycin, isolated in 1944 by Schatz and Waksman, was the first drug to alter the course of spinal tuberculosis, and isoniazid followed in 1952 and rifampicin in the 1960s.
• The British Medical Research Council trials of the 1960s and 1970s showed that ambulatory chemotherapy without routine surgery gave results as good as bed rest and radical debridement, which overturned the prevailing surgical dogma.
• WHO adopted the DOTS strategy in the 1990s, and the Xpert MTB/RIF assay was endorsed in 2010, which shortened the time to microbiological confirmation of spinal disease.
• The consolidated WHO tuberculosis guidelines of 2022 restated the recommended regimen for bone and joint tuberculosis and defined the circumstances in which treatment is extended beyond six months.

Epidemiology

• WHO reported 10.4 million new tuberculosis cases in 2016, of which 46.5 per cent occurred in South-East Asia and 23 per cent in India, and these figures define the population at risk of spinal disease.
• Extrapulmonary tuberculosis accounts for about 15 per cent of all tuberculosis, skeletal tuberculosis for 10 to 15 per cent of extrapulmonary cases, and spinal involvement for about half of skeletal cases.
• The disease is most common in children and young adults in endemic countries, and in high-income settings it appears mainly in migrants, prisoners, homeless people and people living with HIV.
• HIV coinfection increases the risk of extrapulmonary and disseminated tuberculosis, and it also changes the radiographic appearance by producing less reactive bone sclerosis and more widespread involvement.
• Other named risk factors are malnutrition, diabetes mellitus, alcohol use disorder, chronic kidney disease, immunosuppressive therapy and previous untreated tuberculosis.
• Mortality is low when treatment is started before neurological deficit, but diagnosed cases still carry substantial morbidity from kyphosis and residual neurological impairment.
• Diagnostic delay is common because constitutional symptoms are often absent and radiographs are normal early, and delays beyond six months are associated with more severe kyphosis and deficit.
• Named surveillance sources are the WHO Global Tuberculosis Report, which publishes annual incidence by country, and national tuberculosis programmes that report extrapulmonary case notifications.

Pathophysiology

• Mycobacterium tuberculosis reaches the spine haematogenously, either through the arterial circulation or through the valveless Batson venous plexus that connects pelvic and abdominal veins to the vertebral bodies.
• The paradiscal pattern is commonest: infection begins in the metaphyseal bone adjacent to the intervertebral disc, and the disc is spared initially because adult discs are avascular and have no direct blood supply.
• Anterior subperiosteal, central and posterior patterns occur less often, and the anterior subperiosteal type spreads beneath the longitudinal ligament and produces the classic anterior wedging and kyphosis.
• Caseous necrosis and granulomatous inflammation destroy trabecular bone, and the necrotic debris and pus break through the cortex to form a paravertebral or psoas cold abscess with little surrounding inflammation.
• Kyphosis develops when anterior vertebral bodies collapse under axial load, and in children the loss of anterior growth potential causes a progressive deformity that continues after infection is cured.
• Tuli's five-stage classification describes the sequence from early paradiscal involvement to severe kyphosis with neurological deficit, and the paediatric spine-at-risk signs identify children who need stabilisation.

Clinical features

• Back pain is the commonest symptom, is usually localised to the involved segment and worsens with weight bearing, and it may have been present for weeks to months before diagnosis.
• Constitutional symptoms such as low-grade fever, night sweats, weight loss and fatigue are variable and are absent in a large minority, which is one reason the diagnosis is missed.
• Examination shows local tenderness, paraspinal muscle spasm, restricted spinal movement and, in advanced disease, a visible gibbus or rounded kyphosis.
• A cold abscess may present as a painless paravertebral mass, a psoas abscess palpable in the groin, or a discharging sinus tract, and it contains caseous material rather than frank pus.
• Neurological deficit ranges from radicular pain and mild weakness to spastic paraparesis with bladder and bowel dysfunction, and it develops in a substantial minority of patients.
• Named complications are progressive kyphosis, paraplegia, cold abscess with sinus formation, spinal instability, secondary amyloidosis and, in children, severe growth-related deformity.

Diagnosis

• Plain radiography is the first-line image but is only about 15 per cent sensitive in early disease, because 30 to 50 per cent of vertebral mineral must be lost before destruction becomes visible.
• Computed tomography shows bony destruction, sequestra and calcification in cold abscess with near-complete sensitivity, and magnetic resonance imaging is 100 per cent sensitive and about 80 per cent specific for spinal infection.
• Magnetic resonance imaging is the preferred test because it shows disc involvement, epidural extension, cord compression and abscess in one examination, and it guides biopsy and surgical planning.
• Laboratory support is non-specific: erythrocyte sedimentation rate is raised in 60 to 90 per cent of patients and C-reactive protein in about 71 per cent, and both are useful for monitoring response.
• Microbiological confirmation requires CT-guided or open biopsy: acid-fast smear is positive in 25 to 75 per cent, BACTEC culture in about 56 per cent, Lowenstein-Jensen culture in 47 per cent and polymerase chain reaction in 75 to 97 per cent.
• Xpert MTB/RIF detects Mycobacterium tuberculosis with 82.9 per cent sensitivity and 98 per cent specificity, and Xpert MTB/RIF Ultra raises sensitivity to 87.8 per cent with 94.8 per cent specificity.
• The differential diagnosis includes pyogenic spondylodiscitis, brucellar spondylitis, metastatic malignancy, multiple myeloma, fungal spondylitis and spinal sarcoidosis, each distinguished by biopsy, culture or imaging pattern.

Management

• WHO 2022 consolidated guidelines recommend 2HRZE/4HR for six months for most extrapulmonary tuberculosis, with bone and joint disease sometimes extended to nine or twelve months when response is slow.
• The regimen combines isoniazid, rifampicin, pyrazinamide and ethambutol in the intensive phase, and isoniazid plus rifampicin in the continuation phase, with doses adjusted for weight and age.
• Children with bone or joint tuberculosis are treated for twelve months according to WHO guidance, and adherence support is essential because interruption promotes drug resistance and relapse.
• Rifampicin-resistant or multidrug-resistant spinal tuberculosis requires a regimen built on bedaquiline, linezolid, levofloxacin or moxifloxacin and clofazimine under WHO 2022 guidance.
• Surgery is indicated for neurological deficit with cord compression, spinal instability, a large abscess, progressive kyphosis or failure of medical therapy, and options are decompression, debridement and instrumented fusion.
• External bracing and early mobilisation are used for pain control and to limit deformity, and prolonged bed rest is no longer recommended because the Medical Research Council trials showed no benefit.
• Response is monitored clinically and with erythrocyte sedimentation rate or C-reactive protein, and imaging is repeated only when deterioration or a new deficit suggests treatment failure.
• Prevention relies on BCG vaccination of infants in endemic countries, active case finding and treatment of pulmonary tuberculosis, HIV testing and isoniazid preventive therapy for contacts.
• Prognosis is good when treatment precedes neurological deficit, whereas established paraplegia recovers incompletely in a substantial proportion and kyphosis may progress despite microbiological cure.

Research and controversies

• Whether six months is sufficient for spinal tuberculosis is still debated, and trials of shorter or longer regimens have not produced a definitive answer for bone and joint disease.
• The timing of surgery is contested: some centres operate early for any neurological deficit, while others treat medically first and reserve decompression for failure or deterioration.
• Molecular diagnostics are being evaluated for spinal specimens, because Xpert Ultra and targeted next-generation sequencing may confirm diagnosis and resistance faster than culture.
• New tuberculosis vaccines are in late-stage trials, including M72/AS01E, which showed about 50 per cent protection against active disease in a 2019 phase 2b trial, and VPM1002 and MIP/Immuvac in phase 3.
• Shorter all-oral regimens for multidrug-resistant tuberculosis, built on bedaquiline and pretomanid, are being extended to extrapulmonary disease, but spinal-specific outcome data remain limited.