The bacteria Mycobacteria tuberculosis causes tuberculosis. Although tuberculosis, or TB, primarily affects the lungs, it can spread through the blood stream to other sites, a circumstance called extrapulmonary or disseminated tuberculosis. The ends of long bones and the vertebrae are commons sites of extrapulmonary tuberculosis, accounting for up to 35 percent of all cases, according to Drs. Golden and Vikram in their November 2005 article in "American Family Physician."
Tuberculosis can affect any bone, but most commonly it attacks the spine and weight-bearing joints. According to the Merck Manuals Online Medical Library, hands, wrists and elbows often are affected, especially if the patient previously injured them. The type of pain depends on the exact location of the tuberculosis. Spinal tuberculosis, also called Pott's disease, usually affects the thoracic part of the spine, causing constant back pain as the virus degrades the discs cushioning the vertebrae. Tuberculosis in the joints causes an aching pain and stiffness. Tuberculous osteomyelitis, or bone infection, causes constant pain in the bone itself and can cause complications in nearby tissues, such as carpal tunnel syndrome if the wrist is affected.
Tuberculosis of the joints, called articular TB, progressively destroys the joints at the hips or knees. Doctors refer to the condition as "mono-arthritis" because only one joint is affected. The affected joint swells and becomes painful. Movement stiffens, and range of motion is limited. In severe and chronic cases, abscesses develop in the affected joints.
Spinal tuberculosis, if left untreated, can spread from one vertebra to the next, weakening the bones and destroying the cushioning discs between them. In severe cases, the spine can collapse and pinch the spinal cord, causing paralysis of the lower body.
If spinal TB progresses to destruction of the vertebrae and discs, the bones of the spine jut forward. A doctor might be able to feel the displacement as the bones of the spine form a hump called a gibbus.
Patients with TB in their bones might or might not exhibit generalized signs of tuberculosis such as fever, fatigue, night sweats and unexplained weight loss. According to Drs. Golden and Vikram, patients with spinal TB typically experience generalized symptoms, while those with articular TB generally do not. Although about half of all patients with bone TB also have infected lungs, the disease usually is not active there. This means that most patients with bone TB do not suffer from coughing and probably do not suspect that they have tuberculosis. Patients with bone TB are generally not contagious because the disease spreads through coughed up active virus particles.