Tuberculosis is one of the major killer infections with 2.2 million new cases of TB occurring every year and 40% of them occur in South East Asia. India, Indonesia, Bangladesh, Thailand, and Myanmar account for 95% of the cases occurring in South East Asia.
With adventof HIV infections the tuberculosis is showing resurgence. Moreover, due to globalization of the populations, frequent travels, there are higher chances of spread of the disease from non endemic to endemic countries. An endemic country is the one where the disease is constantly present to greater or lesser extent.
Musculoskeletal tuberculosis (Tuberculosis of bone and joints) is also common and responsible majorly for the morbidity, disability and rarley death.
The disease is found more in children, adolescents and young adults, than in the elderly.
The spine is the most common site of involvement, followed by the hip and knee.
In the spine, the usual involvement is vertebral bodies and intervertebral disks in the dorsolumbar regions. Other regions of involvement are the cervical vertebrae, craniovertebral junction, sacrum and sacroiliac joints may be involved. Ribs, pelvic bones, small bones of the and and foot, long bones, sternoclavicular joint, sternum and bursae are also known to get infected.
Sometimes, more than one sites may be affected in same patients and is termed as multifocal skeletal tuberculosis.
How Does The Infection Spread?
Mycobacterium tuberculosis is most common causative organism. The infection in musculoskeltal organs is always secondary to another focus, usually in the lungs or in the mediastinal lymph nodes.
The organisms spread though the blood stream and settles in bone usually near the epiphyseal cartilage in proximity to the synovial membrane. As they proliferate they form what is called ‘tubercle’, the microscopic pathological lesion with central necrosis surrounded by epithelioid cells, giant cells and mononuclear cells.
Two types of microscopic lesions are known
- Caseating exudative type - caseating necrosis and cold abscess formation
- Proliferating type – cellular proliferation with minimal caseation e.g the tuberculous granuloma
The type of lesion formed would depend on how does body deal with bacteria or immunity of the person.
Clinical Features
The onset of the disease is insidious. Patient might have constitutional symptoms like low-grade fever, anorexia and weight loss. If They usually usually precede local symptoms and signs such as pain, tenderness and swelling of the affected part.
However absence of constitutional symptoms does not rule out the possiblity of the disease as it is common for patients to present without any constitutional symptoms.
There might be muscle spasms and discharging sinuses. Discharging sinus is hallmark of chronic infection.
Investigations
Routine laboratory test may be inconclusive. A usual finding is lymphocytosis, raised ESR and raised CRP. Montoux test in non endemic region may indicate presence of tubercular infection.
Xray of the affected part may show destruction of the involved bone or joint. However it is inconclusive in soft tissue affections or in cases where the disease is in early stage and is yet to bring bony changes.
Aspiration of the joint fluid or cold abscess can be investigated to find the mycobacteria. Polymerase chain reaction is a very good test for this purpose. Acid fast bacilli stain is rarely positive in musculokeletal tuberculosis as the bacterial load is not much per se.
Computerized tomography and magnetic resonance imaging are helpful in defining the disease further. While CT is good for bony lesions, MRI defines soft tissues better.
MRI helps to catch the disease early before it is evident on xrays. It may also pick the hidden lesions or lesions like granuloma in spine. It is also helps in assessing complications, assessing response to treatment, provides better delineation of vertebral lesions with adjoining soft tissue involvement and nerve compressions.
MRI is used more frequently than CT.
Biopsy may be needed in cases where a diagnopsis could not be established otherwise. This can be done under the image guidance or by surgery. The material subjected to smear examination, PCR and culture and histopathological examination.
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