Pott's Disease (Spine)

Synonyms: Pott's syndrome, Pott's caries, Pott's curvature, angular kyphosis, kyphosis secondary to tuberculosis, tuberculosis of the spine, tuberculous spondylitis and David's disease

Pott's disease is tuberculous caries or osteitis of the spinal column and must not be confused with Pott's fracture of the ankle.
The source of infection is usually outside the spine. It is most often spread from the lungs via the blood. There is a combination of osteomyelitis and infective arthritis. Usually more than one vertebra is involved. The area most affected is the anterior part of the vertebral body adjacent to the subchondral plate. Tuberculosis may spread from that area to adjacent intervertebral discs. In adults, disc disease is secondary to the spread of infection from the vertebral body but in children it can be a primary site, as the disc is vascular in children.

It is the commonest place for tuberculosis to affect the skeletal system although it can affect the hips and knees too. The usual sites to be involved are the lower thoracic and upper lumbar vertebrae.

The infection spreads from two adjacent vertebrae into the adjoining disc space. If only one vertebra is affected, the disc is normal, but if two are involved the disc between them collapses as it is avascular and cannot receive nutrients. Caseation occurs, with vertebral narrowing and eventually vertebral collapse and spinal damage. A dry soft tissue mass often forms and superinfection is rare.

• Pott's disease is rare in the UK but in developing countries it represents about 2% of cases of tuberculosis and 40 to 50% of musculoskeletal tuberculosis.
• Tuberculosis worldwide accounts for 1.7 billion infections, and 2 million deaths per year.
• Over 90% of TB occurs in poorer countries, but a global resurgence is affecting richer ones.
• India, China, Indonesia, Pakistan and Bangladesh have the largest number of cases but there has been a marked increase in the number of cases in the former Soviet Union and in sub-Saharan Africa in parallel with the spread of HIV.
• The disease affects males more than females in a ratio of between 1.5 and 2:1. In the USA it affects mostly adults but in the countries where it is commonest it affects mostly children.

• Endemic tuberculosis
• Poor socio-economic conditions
• HIV infection

Symptoms

The onset is gradual.

• Back pain is localised
• Fever
• Night sweats
• Anorexia
• Weight loss

Signs

• There may be kyphosis
• A paravertebral swelling may be seen
• They tend to assume a protective upright, stiff position
• If there is neural involvement there will be neurological signs
• A psoas abscess (may present as a lump in the groin and resemble a hernia)

Psoas abscess

A psoas abscess comes from a tuberculous abscess of the lumbar vertebra that tracks from the spine inside the sheath of the psoas muscle.

• Other causes include extension of renal sepsis and posterior perforation of the bowel.
• There is a tender swelling below the inguinal ligament and they are usually apyrexial.
• The condition may be confused with a femoral hernia or enlarged inguinal lymph nodes.

• Pyogenic osteitis of the spine
• Spinal tumours

• Elevated ESR
• Strongly positive Mantoux skin test
• Spinal x-ray may be normal in early disease as 50% of the bone mass must be lost for changes to be visible on x-ray. Plain x-ray can show vertebral destruction and narrowed disc space.
• MRI scanning may demonstrate the extent of spinal compression and can show changes at an early stage. Bone elements visible within the swelling, or abscesses, are strongly suggestive of Pott's disease rather than malignancy. CT scans and nuclear bone scans can also be used but MRI is best to assess risk to the spinal cord.
• A needle biopsy of bone or synovial tissue is usual. If it shows tubercle bacilli this is diagnostic but usually culture is required. Culture should include mycology.

Tuberculosis co-infection with HIV has become common. It is up to 11% in some areas of the UK and over 60% in countries such as Zambia, Zimbabwe and South Africa.

In the developed world, the disease is more common in certain sections of society such as alcoholics, the undernourished, ethnic communities, the elderly, and HIV infected people. The disease is also more common in patients after gastrectomy for peptic ulcer.

The lower thoracic region is the most common area of involvement at 40 to 50%, with the lumbar spine in a close second place at 35 to 45%. The cervical spine accounts for about 10%. The commonest area affected is T10 to L1.

Non-drug

Immobilisation of the spine is usually for 2 or 3 months.

Drugs

This is covered in the article on Management of Tuberculosis.

Surgical

Surgery plays an important part in the management. It confirms the diagnosis, relieves compression if it occurs, permits evacuation of pus, and reduces the degree of deformation and the duration of treatment.¹ However, a Cochrane review found that routine surgery in addition to chemotherapy had not been shown to improve outcome but the problem was that the evidence was poor.² A study from India suggested that surgery is not mandatory.³

• Progressive bone destruction leads to vertebral collapse and kyphosis:
  • The spinal canal can be narrowed by abscesses, granulation tissue, or direct dural invasion. This leads to spinal cord compression and neurological signs (Pott's paralysis).
  • Kyphosis occurs because of collapse in the anterior spine and can be severe
  • Lesions in the thoracic spine have a greater risk of kyphosis than those in the lumbar spine
  • Neurological problems can be prevented by early diagnosis and prompt treatment. It can reverse paralysis and minimise disability.
  • A combination of conservative management and surgical decompression gives success in most patients
  • Late onset paraplegia is best avoided by prevention of the development of severe kyphosis
  • Patients with tuberculosis of the spine who are likely to have severe kyphosis should have surgery in the active stage of disease.⁴
  • The degree of kyphosis, the area of affected vertebrae and lack of sphincter control all correlate with the chance of recovery from paraplegia.⁵
• A cold abscess can occur if the infection extends to adjacent ligaments and soft tissues. Abscesses in the lumbar region may descend down the sheath of the psoas to the femoral trigone region and eventually erode into the skin and form sinuses.

The progress is slow and lasts for months or even years. Kyphosis is common. Prognosis is better if caught early and modern regimes of chemotherapy are more effective. A study from London showed that diagnosis can be difficult and is often late.⁶ Therapy may need to exceed 6 months. Around two thirds of subjects in developed countries are immigrants, as shown from both London⁶ and Paris⁷ and spinal tuberculosis may be quite a common presentation.

As for all tuberculosis. BCG vaccination. Improvement of socio-economic conditions. Prevention of HIV and AIDS.

Percival Pott (not Potts) was born in London in 1716. Having initially been destined for the clergy, he changed his mind and was apprentice to a surgeon at St Bartholomew's Hospital. He was granted the Grand Diploma by the Company of Barber-Surgeons at the age of 22. He developed a private practice and in 1745 he became assistant-surgeon and in 1749 full surgeon at St. Bartholomew's Hospital, remaining there until his retirement in 1787. One cold January morning in 1756, he was making house calls when he was thrown from his horse and sustained an open compound fracture of lower tibia and fibula. He did not accept advice from colleagues who advocated immediate amputation but he had a lengthy convalescence. Whilst immobile he did much writing including describing the management of fractures, including the one that so justly bears his name. In 1788, having caught a cold whilst out visiting patients, he died of pneumonia.
Conditions that bear his name include:

• Pott's aneurysm that is an arteriovenous aneurysm.
• Pott's cancer is a coal tar-induced cancer of the skin that he noted was common on the scrotum of chimney sweeps.
• Pott's disease and the resulting Pott's curvature and Pott's paraplegia.
• Pott's fracture.
• Pott's gangrene is an eponym for mortification of toes and feet due to arterial obstruction in the aged.
• Pott's puffy tumour is a circumscribed oedema of the scalp associated with underlying osteomyelitis of the skull.