Pott's disease overview

# Overview
Pott's disease or Pott disease is a presentation of extrapulmonary tuberculosis that affects the spine. The lower thoracic and upper lumbar vertebrae are most commonly affected. Scientifically, it is called tuberculous spondylitis and it is most commonly localized in the thoracic portion of the spine. Potts disease results from haematogenous spread of tuberculosis from other sites, often pulmonary. The infection then spreads from two adjacent vertebrae into the adjoining intervertebral disc space. If only one vertebra is affected, the disc is normal, but if two are involved, the disc, which is avascular, cannot receive nutrients and collapses. The disc tissue dies and is broken down by caseation, leading to vertebral narrowing and eventually to vertebral collapse and spinal cord compression.

# Historical Perspective
Pott's disease is named after Percivall Pott (17141788), a London surgeon who trained at St Bartholomew's Hospital, London.

# Pathophysiology
Pott's disease occurs usually due to hematogenous spread of tuberculous infection from a pulmonary or genitounrinary site. Pott's disease usually involves more than one vertebra and manifests as a combination of osteomyelitis and arthritis. The involvement of the vertebra can be contiguous or non-contiguous based on the mode of spread.

# Causes
Pott's disease is caused by a bacterium called Mycobacterium tuberculosis or Mycobacterium bovis.

# Differentiating Pott's Disease from other Diseases
Pott's disease presents with chronic back pain, swelling, spine deformity and neurological features in cord compression. All the following conditions present with similar features and must be differentiated from Pott's disease. The differential include: spinal tumors, spinal cord abscess, Mycobacterium kansasii, nocardiosis, septic arthritis, metastatic cancer, multiple myeloma, miliary tuberculosis

# Risk Factors
All the risk factors for developing Pott's disease are the same as risk factors for developing in pulmonary tuberculosis. They include: HIV, overcrowding, immunosuppression, malnutrition, longterm corticosteriod use.

# Natural History, Complications and Prognosis
If left untreated, Pott's disease can cause severe vertebral deformity and collapse resulting in kyphosis, cord compression and paraplegia. With treatment the prognosis is good with improvement in the spine deformity and neurological deficit.

# Diagnosis

## History and Symptoms
The history and symptoms of Pott's disease depends upon the stage of disease, affected site, and presence of complications. Back pain most common symptom of Pott's disease. Other constitutional symptoms include fever, night sweating, anorexia, and weight loss.

## Physical Examination
Physical examination findings suggestive of spinal tuberculosis include local tenderness on the spine, stiffness and spasm of the muscles, cold abscess demonstrates absence of signs of inflammation, limited range of motion, palpable gibbus, spine deformity, kyphosis. Neurologic findings include muscle weakness, quadriplegia, paraplegia, hypotonia, loss of deep tendon reflexes, numbness and paraesthesias.

## X-Ray
Plain radiographs of the spine demonstrate changes suggestive of spinal tuberculosis in majority of the patients. The radiographic changes on plain X-Rays are not evident in the early stages of infection, therefore the changes are present in the late stages of the disease. Findings on the plain radiograph include rarefaction of the vertebral end plates, lytic destruction of anterior portion of vertebral body, collapse of the vertebral body, loss of disc height.

## CT
CT scan of spine provides extent of involvement of the vertebral bodies, intervertebral disks, sclerosis, and osteoporotic vertebral end plates. It is helpful to detect early lesions and is more effective for defining the shape and calcification of soft-tissue abscesses.

## MRI
MRI provides provides the extent of soft tissue involvement and the accurate dimensions of the abscess and its extent.

## Other Imaging Findings
Radionuclide bone scanning may be done, but findings are not specific for Pott's disease.

# Treatment

## Medical Therapy
Pott's disease is treated with  standard  antitubercular therapy for a duration of 6 to 12 months. Compliance to the treatment should be monitored. Response to the treatment is assessed by the improvement of neurological function and reduction of the spinal deformity.

## Surgery
Surgery is not the primary treatment option, but it is preferred in patients unresponsive to medical therapy and worsening neurological function. Surgical debridement is performed in such cases.

## Primary Prevention
Pott's disease can be prevented by controlling the spread of tuberculosis infection. Patients who have a positive PPD test (but not active tuberculosis) may decrease their risk by properly taking medicines to prevent tuberculosis.