Pott's Disease

Tuberculosis or TB is generally considered a lung infection in the developing or underdeveloped world. And while it is true that the tuberculosis bacteria are more prevalent in third-world countries, its incidence in developed nations is on the rise as a result of increased travel and global migration and an increasing population of immunocompromised people. Although TB is preventable and treatable, it remains one of the most deadly infectious diseases. Improper use of anti-tuberculosis medications has led to the development of multi-drug resistant TB which is a global, public health threat as it makes management difficult. 

Extrapulmonary TB refers to TB infection involving organs other than the lungs. Pott’s disease is an example of extrapulmonary TB which can be fatal. 

What is pott’s disease?

Pott's disease also known as Tuberculosis Of The Spine or Spinal TB is an infection of the Vertebral bones of the spinal column (bones of the back). It is caused by a bacteria, Mycobacterium Tuberculosis (TB) and is a dangerous type of extrapulmonary TB infection (infection outside the lungs). It was named after Percival Pott (1714–1788), a surgeon in London.¹ The bacteria is capable of causing destruction to the spine leading to disability, neurological complications like paralysis and mechanical instability of the spine. The treatment involves eradicating the infection from the body with multi-drug chemotherapy and surgery to treat and prevent complications.  

Prevalence

Tuberculosis is a global disease. Currently, it is estimated that about 1.7 billion (26%) of the world’s population is infected by mycobacterium tuberculosis.²

The incidence of extrapulmonary TB, that is tb infection occurring outside the lungs, is 3% among which 10% of cases are skeletal TB (TB infection of the skeletal system).

The most common site of skeletal TB is the spine and constitutes about 50-60% of the skeletal tubercular infection cases.^1,3

Causes and risk factors

Tuberculosis or TB is caused by a bacteria called Mycobacterium Tuberculosis or Tuberculous Bacilli. It is called a fastidious organism which means that it has very complicated nutritional requirements and it will not grow without specific factors present and in specific conditions. Tuberculous bacilli also grow slowly and are capable of remaining dormant (a state in which the organism does not grow or multiply) for a very long time. When the conditions become favourable, it tends to multiply once every 15 to 20 hours.³

Tuberculosis spreads from one person to another through microscopic droplets released into the air by coughing and sneezing. One can get TB from a person who has an active infection if they are in close contact for a prolonged period (several hours).

Tuberculosis infection of the spine is a secondary infection and occurs always as a result of spread of the infection from the disease in another part of the body.

In the majority of cases of spinal TB, the location of the primary infection is the lungs. Infection from the lungs enters the blood and travels to the vertebral bones of the spinal column causing infection. Spinal tuberculosis is not communicable but anyone with spinal TB needs to be further tested to find the site of the primary infection.

Risk Factors:

Some known risk factors for developing TB are:

1. Prolonged exposure to infected patients
2. overcrowding
3. Alcohol dependency
4. Drug abuse
5. Immunocompromised - HIV, diabetes
6. Malnourishment
7. Ethnic minority communities
8. Poverty and low socioeconomic status
9. Elderly
10. Living in areas where TB is endemic

Signs and symptoms

The signs and symptoms of Pott’s disease are variable. They depend on many factors such as:

1. The duration, that is how long the person has had the infection in the spine
2. The severity of the infection
3. The location of the focus of the disease, that is, what part of the spinal column is affected and how many levels are involved
4. The presence of associated complications, like bone and skeletal deformities and neurological deficits (impairment due to damage of the spinal cord) 

The usual sites of involvement are the lower thoracic and upper lumbar vertebrae that is the middle and lower back. Usually, more than one vertebra is involved. The infection can spread to adjacent upper and lower vertebras or it can also skip levels. It can also involve the intervertebral discs. Destruction of vertebral bones and disc spaces causes instability of the spine and deformity.

Constitutional symptoms of TB

Constitutional signs and symptoms of a tuberculosis infection like weight loss, decreased appetite, drenching sweats in the night, low-grade fever, fatigue and malaise are not as commonly seen in cases of Pott’s disease or spinal TB as they are seen in pulmonary TB (infection of the lungs)

Uncomplicated pott’s disease:

The Tuberculous bacilli (bacteria) can stay inside the body in a resting form for a long time without causing any signs of infection. When the circumstances become favourable for the bacilli, it starts to multiply and produce symptoms.

Initially in the absence of any complications people suffering from spinal TB complain of and present with back pain and tenderness.

This back pain can be related to the disease itself (the infection leads to inflammation of the area and causes pain) or it could be due to destruction of the bones. This can in turn cause instability of the spine. The pain is gradual in onset and localised at the site of the infection.

Back pain on rest is characteristic of spinal TB but it can also present as pain from the back going to the arms or legs. This type of pain is called radicular pain. 

Complicated pott’s disease:

Prolonged standing infection causes involvement of multiple levels of the vertebra. The disease. Progressive destruction leads to the following complications:

1. Instability of spinal column – there is displacement and abnormal movement of spinal structures. This can cause low back pain, stiffness, muscle spasms and a feeling like the back is “giving way” during movement. The pain is worse with activities like bending and twisting and lifting heavy objects
2. Deformity of spinal column – Kyphotic deformity or kyphosis occurs secondary to spinal TB. It is an abnormal curvature of the spine where the upper back is more rounded forward than normal

The deformity is worse and progresses even after treatment in children as their spines are immature and more flexible 

3. Neurological deficit: The vertebral column or spinal column encloses and protects the spinal cord. The spinal cord is a part of the central nervous system and is a long thin tube that extends downward from the base of the brain. It is a pathway for messages sent by the brain to the body and from the body to the brain

The spinal cord can get affected causing neurological symptoms. In the initial stages, there is weakness of the muscles, and later on, it progresses to complete paralysis of the lower body. This paralysis is known as Pott's paraplegia.

4. Cold abscess – A cold abscess is an abscess without the characteristic signs of inflammation(redness, heat, swelling and pain). The pain caused by such an abscess is only vague. An abscess is a collection of pus inside a walled cavity. This can occur when infectious material slowly spreads to the adjacent ligaments and tissue and gets collected there

Diagnosis:

Imaging:

1. Plain X-ray of the spine – shows sign of late disease including bone destruction and disc prolapse
2. CT scan of spine – shows disease at an earlier stage compared to x-ray, but is not accurate for determining the extension of infection into adjacent tissues and spinal cord (neurological) involvement
3. MRI with contrast of spine – the most effective tool to diagnose spinal TB. It can also show the extension of infection into adjacent tissues and ligaments as well as determine the extent of spinal cord(neurological) involvement
4. Nuclear imaging

Image-guided biopsy:

CT scan can help guide experts in taking a sample from the site of infection in the spinal column. This sample is sent to the laboratory to test for TB. The following tests can be performed on them to confirm the diagnosis:

• Acid Fast Bacilli (AFB) smear and culture
• Polymerase chain reaction (PCR)

Other test

1. Erythrocyte sedimentation rate (ESR): It is raised in TB and a decrease in its level shows a response to treatment
2. Gene Xpert MTB/RIF: this test helps to check for resistance to rifampicin. It is also a recommended test by the WHO to confirm TB in patients with compromised immune system such as HIV
3. Chest X-Ray and sputum culture: helps to diagnose the presence of co-existing  pulmonary TB 

Treatment:

The goal of treatment of spinal tuberculosis or Pott’s disease is to:

1. Eradicate the infection from the body
2. Correct and halt any instability and deformity
3. Treat and prevent the development of neurological complications.

Treatment of uncomplicated spinal TB:

In the absence of severe deformity and neurological complications, the mainstay of treatment of spinal TB is chemotherapy and orthosis (external bracing) and prolonged rest.

Chemotherapy for Pott's disease:

The tuberculous bacilli can exist in multiple forms inside the body. It can be

•  Intracellular (inside the cells)
•  Extracellular (outside the cells)
•  Dormant form (resting and not dividing)
•  Rapidly multiplying forms

In order to attack the bacilli in the various forms and stages that it can exist in, multi-drug treatment called Antituberculous Treatment or ATT is recommended. 

Anti Tuberculous Treatment or ATT consists of the following four drugs:

1. Isoniazid (INH)
2. Rifampicin
3. Ethambutol
4. Pyrazinamide

Other second-line drugs are indicated when there is resistance or poor tolerance to the first-line drugs.

The duration of ATT in spinal Tb is controversial. The WHO recommends 6 months of multidrug anti tubercular therapy in two phases:

• Initiation phase: The initiation phase includes 2 months of four- or five-drug treatment (isoniazid, rifampicin, pyrazinamide, ethambutol, and/ or streptomycin)
• Continuation phase: The initiation phase is followed by the continuation phase of four months of therapy with a two-drug regimen including isoniazid and rifampicin

The American Thoracic Spine Society recommends a regimen involving 9 months of treatment with the same drugs ("continuation" phase extending for a period of 7 months). The Canadian Thoracic Society recommends treatment for 9 to 12 months duration.³

The National Institute for Health and Care Excellence (NICE) recommends 6 months duration of ATT in active Pott’s disease without neurological complications and an extension of therapy to 10 months duration in cases of neurological complications.⁴

Multidrug resistance

Multi-drug resistant TB or MDR-TB is defined as a TB infection which is resistant to isoniazid (INH) and rifampicin. Extensively drug-resistant TB (XDR-TB) is defined as infection resistant to INH and rifampicin, along with resistance to a fluoroquinolone (class of antibiotic used in ATT) and at least one injectable second-line medication.

Resistance to ATT is a growing problem, especially in the areas where TB is endemic and it makes it extremely difficult to eradicate the disease from the population. It stems from noncompliance with ATT therapy. Other causes include:

• Inappropriate medical prescription
• Poor quality anti-TB drugs
• Failure to complete treatment
• Interruption in treatment
• Lack of national TB control programs 

Directly observed therapy or DOT can ameliorate resistance and is recommended by the WHO. In this therapy, the patient takes every dose of the TB medication under the direct observation of a healthcare worker.

Spinal orthosis:

External bracing and support using spinal orthosis is used to 

• Control pain
• Prevent deformity and reduce the occurrence of kyphosis

Treatment for complicated Spinal TB:

In patients suffering from complicated spinal TB, surgical intervention is required in addition to chemotherapy.

The chemotherapy is done both before and after the surgery. Performing surgery in active disease provides a good outcome.

Sugary for Pott's disease

Surgical intervention is necessary for the following situations:

1. Failure to respond to chemotherapy after 3-6 months
2. Recurrence of the disease
3. Severe neurological weakness at presentation
4. Neurological deficit not improving despite a course of ATT
5. Neurological deficit getting worse despite a course of ATT
6. Deformity example kyphosis
7. Debilitating pain
8. Instability

The objectives of surgical intervention include:

• drainage of any abscess present – can be done through a minimally invasive or open procedure.
• debridement of infected tissues. Debridement is the surgical removal of any dead, damaged or infected tissue to improve healing of the remaining healthy tissue
• stabilisation of vertebrae
• Correction of deformity

Outlook

Early diagnosis and treatment is crucial in ensuring a good outcome in Pott’s disease. The treatment progress is slow and the disease can last for months or even years. Complicated spinal tuberculosis (associated deformity, neurological involvement, instability) has a poorer outcome compared to uncomplicated disease. Other factors that influence the outcome are:

1. Extremes of age, very young and very old people have poor outcome and more complications
2. Have a weak immune system - HIV, alcohol and drug abuse
3. Overcrowding
4. Malnutrition
5. Poverty and low socioeconomic status
6. Poor compliance to ATT
7. Inability to tolerate ATT (deranged liver function)

Generally, complicated Pott’s disease (with associated deformity, instability or neuro deficit) has a poorer prognosis as compared to an uncomplicated disease. Other important prognostic factors include age (poorer outcome in extremes of ages),⁷ immunodeficiencies (HIV, alcohol, drug abuse), overcrowding, malnutrition, poverty, and lower socio-economic situation. Poor tolerance to ATT and poor compliance is a major factor for drug failure in TB management. 

Conclusion:

Pott’s disease or spinal tuberculosis is a destructive form of extrapulmonary tuberculosis. Its incidence is increasing in developed nations. The tuberculosis bacteria spread from a primary site of infection, most commonly from the lungs, to the vertebral bones of the spinal column through blood. It infects and destroys the vertebral bodies, particularly the anterior part. From there it spreads into the adjacent intervertebral disc space leading to collapse of the elements of the spine and development of instability and deformity. Spinal tuberculosis can occur in multiple levels of the spinal column, in a sequence or as skipped levels. The thoracic region of the vertebral column (spinal column at the level of the chest) is most frequently affected. The signs and symptoms of uncomplicated spinal TB are back pain which is localised and spinal tenderness. The destruction of the spinal column can cause complications like instability, kyphotic deformity, formation of a ‘cold’ abscess and neurological deficit ranging from mild weakness in limbs to paraplegia (complete paralysis of the lower body ). The diagnosis of spinal TB is made by observing the destruction of the spinal column on MRI scan and on neuroimaging-guided needle biopsy and histopathology. Other tests for diagnosing the primary site of TB infection like blood tests, chest X-ray and sputum test are also performed. In the absence of complications, spinal TB is a medical disease and is treated using a combination of medicines called antituberculous treatment (ATT)/ chemotherapy. The duration of treatment can range from 6-12 months. Surgery is required in the presence of complications like severe deformity, neurological deficits and recurrent disease and lack of response to medical treatment. The outcome of the disease is generally good when diagnosed and treated early.