Spinal Tuberculosis (Pott Disease)

Spinal tuberculosis (Pott disease, tuberculous spondylitis) is infection of the vertebrae and intervertebral discs with Mycobacterium tuberculosis, usually from haematogenous spread of pulmonary or other primary infection. It is the commonest form of skeletal tuberculosis, and accounts for about half of all bone and joint tuberculosis.

Skeletal tuberculosis occurs in about 1 to 3% of patients with tuberculosis, and spinal disease in about 1 to 2% of all cases. It affects any age, with peaks in children and in adults of 30 to 50 years in high burden countries and in older adults in low burden settings. The thoracolumbar junction is the commonest site, then the lumbar and thoracic spine. HIV infection, malnutrition, diabetes, immunosuppression, alcohol use disorder and migration from endemic areas are risk factors.

Complications are vertebral collapse with kyphosis (gibbus), cold abscess (paravertebral, psoas, epidural), neurological deficit (Pott paraplegia in 10 to 40%), spinal instability, and chronic pain. Most patients recover with antituberculous treatment, and neurological recovery is good if treated early.

Pathophysiology.

Bacilli seed the anterior part of the vertebral body (paradiscal, central, anterior or appendiceal pattern), then spread under the anterior longitudinal ligament to adjacent vertebrae. Unlike pyogenic infection, the disc is preserved until late because tubercle bacilli lack proteolytic enzymes. A caseating granuloma forms, bone collapses anteriorly, and a cold abscess tracks along fascial planes. Neurological injury results from compression by pus, granulation tissue, sequestrum or disc, from kyphotic deformity, and from vasculitis.

Insidious back pain over weeks to months, night pain, spinal stiffness and tenderness, low grade fever, night sweats, weight loss, malaise, and a palpable kyphosis or a paravertebral or psoas swelling. Neurological symptoms include weakness, sensory loss and sphincter dysfunction. Children may show a stiff, flexed back and refusal to walk.

Examine for gibbus, paravertebral swelling, psoas abscess (flexed hip), neurological state, chest, lymph nodes, and other sites of tuberculosis.

• ESR (raised in over 90%) and CRP; full blood count; HIV test; HbA1c; liver and renal function before treatment.
• Chest radiograph (abnormal in 30 to 50%); sputum or gastric aspirate for acid fast bacilli, culture and nucleic acid tests when indicated.
• MRI of the whole spine with gadolinium (the key test): vertebral body oedema and destruction, relatively preserved disc until late, paravertebral and epidural abscess, thin walled rim enhancement, skip lesions, and cord compression. CT shows bone destruction, calcification and sequestra.
• Tissue diagnosis: image directed or open biopsy or abscess aspirate for histology (caseating granuloma), acid fast stain, culture (positive in 50 to 70%), and nucleic acid amplification with rifampicin resistance testing (positive in 70 to 90%). Culture allows drug susceptibility testing.
• Interferon gamma release assay or tuberculin skin test supports but does not confirm infection.

Differential diagnosis.

• Pyogenic vertebral osteomyelitis and brucellosis.
• Metastasis, lymphoma and myeloma.
• Fungal spondylitis and sarcoidosis.
• Osteoporotic compression fracture and Scheuermann disease.

Antituberculous chemotherapy is the cornerstone; surgery is added for selected patients.

Chemotherapy (start after biopsy when the patient is stable; start empirically if neurological deficit or sepsis).

• Intensive phase (2 months): rifampicin 10 mg/kg orally daily (usual adult dose 600 mg for weight 50 kg or over, 450 mg under 50 kg; maximum 600 mg), isoniazid 5 mg/kg daily (maximum 300 mg), pyrazinamide 25 mg/kg daily (usual 1500 mg for 40 to 55 kg, 2000 mg for 56 to 75 kg; maximum 2 g) and ethambutol 15 mg/kg daily (maximum 1600 mg).
• Continuation phase: rifampicin and isoniazid daily for 7 to 10 months (total 9 to 12 months; extended to 12 to 18 months for complex disease, slow response or poor drug penetration).
• Pyridoxine 10 to 25 mg orally daily with isoniazid (up to 50 mg daily in pregnancy, HIV, diabetes, malnutrition, renal failure or alcohol use).
• Monitor liver function at baseline, at 2 weeks, and monthly. Stop drugs and review if ALT rises above 3 times the upper limit with symptoms or above 5 times without.
• Also monitor visual acuity and colour vision with ethambutol, uric acid and joint pain with pyrazinamide, and full blood count.
• Avoid ethambutol in optic neuritis; adjust ethambutol and pyrazinamide dose frequency at creatinine clearance under 30 mL/min.
• Rifampicin interacts with many drugs (warfarin, direct oral anticoagulants, contraceptives, antiretrovirals, antiepileptics, corticosteroids); review all medicines.
• HIV co-infection: start antiretroviral therapy within 2 weeks if CD4 count is under 50 cells/microlitre and within 8 weeks otherwise; with dolutegravir, raise the dose to 50 mg twice daily while rifampicin is given; avoid boosted protease inhibitors with rifampicin.
• Drug resistant disease: needs a specialist regimen based on susceptibility (for example bedaquiline, linezolid 600 mg daily, levofloxacin 750 to 1000 mg daily, and a fourth agent), for 9 to 20 months or longer.
• Corticosteroids are not routine for spinal disease; they are given for tuberculous meningitis and may be used with severe paradoxical reactions.

Surgery (about 10 to 20% need it). Indications are:

• progressive or severe neurological deficit (especially with a large abscess or sequestrum)
• spinal instability
• progressive or severe kyphosis (over 30 to 60 degrees or progressing)
• a large abscess not responding to treatment
• diagnostic uncertainty requiring biopsy
• failure of medical therapy

Procedures:

• anterior debridement with strut or cage reconstruction
• posterior instrumentation with decompression (one stage posterior approach is increasingly used)
• abscess drainage

Children need long follow up for kyphosis progression.

Bracing and rest. A brace or bed rest for pain and stability in the early phase, then graded mobilisation.

Perioperative care.

• Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision.
• Tranexamic acid 15 mg/kg (maximum 1 g) intravenously over 10 minutes before incision.
• Enoxaparin 40 mg subcutaneously once daily from 24 to 48 hours after surgery while immobile (20 mg at creatinine clearance under 30 mL/min).

Analgesia.

• Paracetamol 1 g orally every 6 hours (maximum 4 g daily; 3 g daily with hepatic impairment, which is common on antituberculous drugs).
• Oral morphine 5 to 10 mg every 4 hours as needed for severe pain (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2).
• Avoid NSAIDs with kidney or liver impairment.

Monitoring.

• Clinical and neurological review at 2 weeks, then monthly in the first 3 months, then every 3 months.
• CRP and ESR monthly.
• MRI at 3 to 6 months or sooner for deterioration (abscess and soft tissue changes can look worse in the first months, a paradoxical reaction).
• Radiographs for kyphosis every 3 to 6 months.
• Adherence support or directly observed therapy.
• Follow up for at least 12 months after treatment.

Referral and escalation. Refer any suspected spinal tuberculosis for MRI, biopsy and specialist infectious disease care. Emergency referral for neurological deficit, rapidly progressive kyphosis, or sepsis. Notify public health services and screen household contacts.

Special groups.

• Children: dosing by weight (rifampicin 15 mg/kg, isoniazid 10 mg/kg, pyrazinamide 35 mg/kg, ethambutol 20 mg/kg); monitor kyphosis until maturity.
• HIV: co-ordinate antiretroviral timing; watch for immune reconstitution inflammatory syndrome.
• Pregnancy: rifampicin, isoniazid and ethambutol are used; pyrazinamide is used in many settings; pyridoxine supplementation.
• Liver or kidney disease: specialist regimen adjustment and close monitoring.