Spinal Tuberculosis (Pott's Disease)

Spinal tuberculosis (Pott's disease) is the most common form of skeletal tuberculosis, first described by Percivall Pott in 1779. It is a significant cause of morbidity, particularly in endemic regions, and remains important in low-incidence high-income settings because of immigration.

Who and where. Spinal TB accounts for 50% of all skeletal TB and is the second most common form of extrapulmonary TB. It can occur at any age but peaks in the second and third decades, with a male to female ratio of approximately 1.5:1. The thoracolumbar junction (T10-L2) is most commonly affected, and approximately 10-15% of patients have skip lesions, non-contiguous involvement at another level.

Global burden. Incidence, and the risk factors behind it, differ with how endemic the setting is:

Route of infection. Haematogenous spread from a pulmonary focus is the most common route, with arterial dissemination to the vertebral bodies. The paradiscal arteries supply adjacent vertebrae, which is how the paradiscal type arises, and Batson's venous plexus may facilitate spread.

Secondary spread. The infection spreads by four routes:

• Subligamentous, under the anterior longitudinal ligament (ALL)
• Epidural, causing cord compression
• Paravertebral, forming a cold abscess
• Along the psoas sheath, as a psoas abscess; a bilateral psoas abscess is a characteristic pattern of tracking

View larger

The lesion. Granulomatous inflammation with caseous necrosis destroys bone and forms sequestra, with minimal new bone formation, unlike pyogenic infection. The destruction is gradual and less explosive than in pyogenic disease, and an abscess may form within the vertebral body itself (intraosseous abscess). Granulation tissue proliferates, and healing brings fibrosis.

The cold abscess. Characteristic of TB, it contains caseous, cheese-like material, not pus. It collects in the paravertebral, epidural and psoas spaces and can track along fascial planes.

Patterns of involvement. Four anatomical types are recognised.

Paradiscal (50-75%). The most common pattern: the adjacent vertebral bodies and the intervening disc, reached by arterial spread through the paradiscal arteries. The disc is destroyed late, unlike in pyogenic infection, and the disease may extend to multiple levels.

Central. Isolated involvement of one vertebral body, with concertina collapse; it may produce an ivory vertebra. Disc height is spared initially.

Anterior subligamentous. The infection spreads under the ALL over several levels, scalloping the front of the bodies, and can produce skip lesions. Extensive as it is, it may spare vertebral integrity initially.

Posterior (2-10%). Involves the neural arch (pedicle, lamina, spinous process). It is more common in the lower lumbar spine and may cause early neurological deficit.

Presentation. The onset is insidious, typically over weeks to months, where pyogenic infection is acute over days to weeks.

History. Beyond the duration and the constitutional symptoms (weight loss, night sweats, low-grade fever), establish:

• Neurological symptoms: weakness, numbness, bowel and bladder
• Contact history (TB exposure)
• Country of origin and travel
• Immunocompromise: HIV, diabetes, immunosuppressants
• Previous TB treatment

The spine. Look for the gibbus, an angular kyphosis: a short, sharp angulation over one or two segments, unlike the smooth, rounded curve of osteoporotic or postural kyphosis. Then feel for localised tenderness and paraspinal muscle spasm, note the restricted range of motion, and search the paravertebral region, groin and flank for a cold abscess.

View larger

The cold abscess on examination. A non-tender, fluctuant swelling that lacks the heat, redness and pain of acute inflammation and the systemic toxicity of a pyogenic abscess; that absence is characteristic. It may track to distant sites, such as the groin in a psoas abscess, and a groin or iliac fossa swelling with back pain is spinal TB until the MRI says otherwise.

Neurological examination. Record motor power by myotome, the sensory level and the reflexes. Look for long tract signs (spasticity, clonus, Babinski), assess bladder and bowel function, and watch the gait.

Systemic examination. Look for lymphadenopathy, pulmonary findings of primary TB, a peripheral cold abscess and signs of other organ involvement.

Blood and microbiology. The essential tests:

Plain radiographs. First-line, and late. They become positive only when 50% of the trabecular bone has been destroyed, which may take 4-6 months, and then show vertebral destruction, collapse and kyphosis. They are also the reminder to look at the chest.

View larger

MRI is the modality of choice. It has high sensitivity for marrow oedema, paravertebral and epidural abscess and cord compression, and detects disease earlier than plain films, months before they become positive. It is essential for the soft tissues and identifies skip lesions, so always image the whole spine. The findings:

• T1: hypointense marrow signal
• T2/STIR: hyperintense marrow oedema
• Contrast: rim enhancement of the abscess
• Epidural extension, causing cord compression
• Skip lesions
• Psoas and paravertebral abscess

View larger

The disc sign is real but weak. "TB spares the disc" is the most-quoted discriminator from pyogenic spondylitis and the least powerful one, so be precise about which disc finding you mean. Disc signal changes in 82% of tuberculous spondylitis against 95% of pyogenic: the disc is involved in the large majority of TB and is not "preserved" in any absolute sense. What is relatively spared is disc height, lost in only 22% of TB against 59% of pyogenic.

Why height survives. The mycobacterium lacks the proteolytic enzymes that let pyogenic organisms digest the nucleus, so the disc is inflamed but not destroyed. The mechanism explains height preservation, not signal normality, and late in the disease the disc narrows secondary to collapse of the adjacent bodies.

View larger

Lead with the structural signs. A thin, smooth abscess wall and subligamentous spread under the ALL separate the two infections far more sharply than the disc, followed by epidural extension and vertebral collapse. Add the clinical tempo. The frequencies below are pooled from a meta-analysis.

View larger

CT. Superior bone detail, the pattern of bony destruction, and guidance for biopsy, but it is still blind to the epidural collection. Its particular contribution is calcification within the paravertebral soft tissue, a slow-disease marker: strongly suggestive of a chronic granulomatous process and effectively ruling out an acute pyogenic collection, but not pathognomonic for TB, since brucellar and fungal abscesses also calcify. CT is for calcification, biopsy planning and the chest.

View larger

Tissue diagnosis. Obtain tissue by CT-guided percutaneous biopsy, open surgical biopsy or abscess aspiration. Histology looks for caseous necrosis, epithelioid granulomas and Langhans giant cells, and the specimen also goes for AFB staining and PCR (GeneXpert). Biopsy is indicated in particular for:

• Atypical presentation
• Negative Mantoux/IGRA
• Suspected MDR-TB
• Excluding malignancy
• Failed empirical treatment

Differential diagnosis. The discriminating features and the key test for each:

The trap. Metastatic disease and myeloma also spare the disc, so disc preservation alone does not confirm infection. A paravertebral cold abscess and subligamentous spread point to TB, whereas pedicle destruction without an abscess favours malignancy.

View larger

Algorithm

View larger

Medical first. Antitubercular therapy (ATT) alone succeeds in 85-90% of cases when the neurological deficit is not severe, and even with neurology medical treatment is often effective. Surgery is reserved for progressive neurology, instability, failure of medical treatment and severe kyphosis.

Medical ManagementSurgical IndicationsSurgical Techniques

The regimen. Four drugs in an intensive phase, then two in continuation:

Intensive

Duration

2 months

Drugs

HRZE (4 drugs)

Continuation

Duration

4-10 months

Drugs

HR (2 drugs)

Phase	Duration	Drugs
Intensive	2 months	HRZE (4 drugs)
Continuation	4-10 months	HR (2 drugs)

Doses are weight-based, with a maximum for each drug:

• H (Isoniazid): 5 mg/kg (max 300 mg)
• R (Rifampicin): 10 mg/kg (max 600 mg)
• Z (Pyrazinamide): 25 mg/kg (max 2 g)
• E (Ethambutol): 15 mg/kg (max 1.2 g)

How long. The continuation range reflects a genuine split in guidance. WHO endorses a 6-month regimen for drug-susceptible disease (2 months HRZE then 4 months HR), supported by the MRC ambulant-chemotherapy RCT, in which 6 months of isoniazid plus rifampicin gave a 94% favourable outcome at 10 years. CNS/spinal-focused guidance (e.g. the British Infection Society) recommends 12 months: 2 months of four drugs then at least 10 months of isoniazid and rifampicin. Many spinal units extend to 9-12 months in extensive or slow-responding disease.

Drug-resistant disease. MDR-TB requires substantially longer, specialist-directed treatment, with second-line drugs (fluoroquinolones, injectables) over an extended 18-24 months.

Monitoring. Check LFTs, uric acid and visual acuity at baseline, and LFTs monthly through the intensive phase. The response is slow, taking weeks to show. Follow it clinically and by the ESR trend, and look for radiological healing with MRI at 6 months.

Hepatotoxicity Risk

Risk factors for hepatotoxicity include age more than 35, pre-existing liver disease, alcohol use, and concurrent hepatotoxic medications. Stop ATT if ALT rises more than 5x ULN or symptoms develop.

View larger

Absolute indications

1. Progressive neurological deficit despite ATT
2. Severe or worsening kyphosis (more than 40-50 degrees)
3. Spinal instability
4. Large abscess requiring drainage
5. Tissue diagnosis (when needed)
6. MDR-TB with poor response

Relative indications

• Moderate neurological deficit with poor recovery
• Significant kyphosis (more than 30 degrees)
• Large psoas abscess
• Bony instability
• Severe pain despite medical treatment

Timing. Rapidly progressive neurology is urgent. Stable neurology with a mechanical problem is semi-elective, and deformity correction after healing is elective.

What the operation must achieve. Surgery combined with ATT improves neurological recovery and prevents deformity progression in selected cases.

Decompression

Approach

Anterior or posterior

Debridement

Approach

Remove caseous material

Stabilisation

Approach

Instrumented fusion

Deformity correction

Approach

Kyphosis correction

Tissue for diagnosis

Approach

Histology and culture

Goal	Approach
Decompression	Anterior or posterior
Debridement	Remove caseous material
Stabilisation	Instrumented fusion
Deformity correction	Kyphosis correction
Tissue for diagnosis	Histology and culture

Anterior approach. The traditional approach for thoracic and lumbar disease. It gives direct access to the disease focus, effective debridement and anterior reconstruction; the Hong Kong technique is radical debridement with a strut graft.

Posterior approach. Pedicle screw instrumentation with posterior decompression (costotransversectomy), combined with anterior debridement. It is the less morbid approach and better for multilevel disease.

Combined anterior-posterior. Indicated for severe instability. It allows circumferential debridement and optimal correction, at the cost of higher morbidity.

Minimally invasive. Video-assisted thoracoscopic surgery and percutaneous instrumentation reduce morbidity in selected cases.

Implants. Titanium is preferred: MRI compatible with minimal artefact and good biocompatibility, and it can be used to instrument in active infection. Fusion uses autograft (iliac crest, rib), a titanium mesh cage, a strut graft (fibula) or bone graft substitutes.

After surgery. Continue ATT for the full course, monitor wound healing and the neurology, brace (practice varies), and rehabilitate. Surgical outcomes are generally good when combined with appropriate medical therapy.

Disease-related complications and their management:

Pott's paraplegia of early onset. In active disease the paraplegia results from reversible anterior compression by an epidural cold abscess, caseous granulation tissue, or sequestrum and debris. It carries the better prognosis and usually recovers well with decompression and ATT.

Pott's paraplegia of late onset. It appears years after the disease has healed and carries a worse prognosis. The cord is compressed by the internal salient (internal gibbus), the bony ridge of the healed kyphus projecting into the canal at the apex, and by dural and peridural fibrosis, with the cord stretched and draped over the bony ridge. Rarely the cause is reactivation or, late, cord atrophy or syringomyelia. Treatment is anterior decompression that removes the internal salient: an anterior problem needs an anterior solution.

Preventing kyphosis. Early recognition and appropriate treatment can prevent severe kyphosis. Consider early surgery in children with significant vertebral destruction to prevent late kyphotic deformity.

Complications of treatment. On the medical side, hepatotoxicity (2-10%), drug reactions and interactions, and the development of MDR. Surgery risks infection, neurological injury, hardware failure, pseudarthrosis and recurrence.

Long-term sequelae. Residual kyphosis, chronic pain, residual neurological deficit, adjacent segment disease and, in children, growth disturbance.

Neurological recovery depends on how severe the deficit is at presentation.

What favours recovery. A short duration of deficit, incomplete paraplegia, younger age, compression by soft tissue rather than bone, and early initiation of treatment. The extent of vertebral destruction also bears on the prognosis.

Medical treatment alone. Healing takes 6-12 months, and residual kyphosis follows in 30-50%.

Combined medical and surgical treatment. Neurological improvement in 70-90%, fusion in 90-95%, and the deformity correction is maintained.

Long-term prognosis. The outcome turns on the extent of the initial disease, the timing of treatment, the adequacy of ATT, the surgical technique and patient compliance. Light activities resume at 3-6 months and full activities at 6-12 months, depending on neurological status.

Global Epidemiology

Tuberculosis remains a leading infectious cause of death worldwide, with around 1.3 million deaths annually. Spinal TB is the most common musculoskeletal manifestation, affecting roughly 1 to 2% of all cases of TB, and skeletal involvement occurs in approximately 10% of those with active disease. Burden is concentrated in South and South-East Asia, Sub-Saharan Africa and the Western Pacific. In low-incidence high-income settings, the overwhelming majority of cases are in people born in high-burden countries, frequently presenting as reactivation of latent infection years after migration. HIV co-infection, which is endemic in parts of Sub-Saharan Africa, adds substantially to both the burden and complexity of management.

Major Guidance Side-by-Side

The most important guideline divergence to recognise is duration: WHO endorses a 6-month regimen for drug-susceptible disease (supported by the MRC ambulant-chemotherapy RCT), whereas neurological/CNS-focused guidance such as the British Infection Society recommends a longer 12-month course (2 months of four drugs then at least 10 months of isoniazid and rifampicin) for spinal and CNS disease. Many spinal units extend treatment to 9-12 months in extensive or slow-responding disease.

Diagnostic Standards

A tissue diagnosis (culture, histology and nucleic-acid amplification) is the worldwide gold standard before committing a patient to prolonged therapy, and is especially important in low-prevalence settings and to detect drug resistance. Xpert MTB/RIF on bone or abscess material gives rapid results and simultaneously reports rifampicin resistance, but its sensitivity on bone is only moderate when used alone, so it should be paired with histopathology and culture rather than replacing them.

Practice Variation by Resource Setting

In resource-limited high-burden regions, empirical antitubercular therapy on clinical and radiographic grounds is common where biopsy is impractical, and a conservative "middle-path" approach (chemotherapy with selective surgery) predominates. In low-incidence settings, mandatory public-health notification, contact tracing, directly observed therapy for adherence, and multidisciplinary input from infectious diseases, spinal surgery, radiology and rehabilitation are standard.