A 46-year-old African man who recently immigrated here presents with chronic back pain for three months, which has worsened over the past week. He denies any known past medical problems, IV drug use, trauma, abdominal pain, and bladder or bowel dysfunction.
He complains of bilateral numbness in the buttocks and upper posterior legs, fever, and night sweats that has lasted for weeks. He has focal lumbar tenderness on palpation; otherwise, this exam is unremarkable. How would you evaluate this patient?
Diagnosis: Pott's Disease
Tuberculosis is the most deadly infectious disease in the world after HIV, affecting an estimated 30 percent of the world's population, according to the World Health Organization. Pott's disease, the result of reactivation of latent TB infection in the bone or soft tissues, is rare in developing countries, but is still a public health threat in the developing world. Pott's was thought to afflict many historical figures including the Hunchback of Notre Dame, Anna Roosevelt Cowles (sister of Theodore Roosevelt), and English poet Alexander Pope.
TB is most commonly caused by inoculation with Mycobacterium tuberculosis but also with M. africanum and M. bovis. TB is spread by inhalation of respiratory droplets from an infected individual. These droplets seed the host (pulmonary and at times extrapulmonary), and result in mild upper respiratory symptoms that are typically self-limited and often go undiagnosed. (New Eng J Med 1991;324:289.) Of those who become inoculated, approximately one in 10 develops an infectious form of the disease. If left untreated, 50 percent of those infected will die from the disease. The most common cause of reactivation of TB is HIV co-infection.
Via hematogenous spread, TB can infect nearly every organ in the body, resulting in myriad infectious diseases. Pulmonary TB is the most common, given the respiratory route of transmission and initial site of inoculation. Infection of extrapulmonary body sites is common, including joints or bone (10%). The risk of developing bony infection is increased in those infected with HIV. (Spine 1997;22:1791.) All bones of the body can be infected with M. tuberculosis, but the spine is by far the most common (50%). (J Bone Joint Surg Am 1996;78:288.)
Nearly 50 percent of cases of Pott's disease (tuberculous spondylitis) affect the thoracic spine, 40 percent the lumbar, and 10 percent the cervical spine. More than 60 percent of people diagnosed with spinal TB were not previously diagnosed with pulmonary TB, making the diagnosis challenging in many cases. (Am Rev Respir Dis 1987;135:1137.) When two adjacent vertebrae are infected, the avascular intervertebral disk (in adults) is at risk for caseating destruction (osteomyelitis) and subsequent vertebral collapse and spinal cord and nerve damage.
Patients with Pott's disease most commonly present with focal pain in the spine, but they also may complain of constitutional symptoms including fever, chills, weight loss, malaise, anorexia, and fatigue. Neurological symptoms are present in 50 percent of patients. Advanced cases can lead to paraplegia (i.e., Pott's paraplegia). If spinal cord compression (i.e., cauda equine) has occurred, patients may present with focal lower extremity weakness, paresthesias, retention, incontinence, or erectile dysfunction. Most patients with symptomatic spinal Pott's have some degree of kyphosis. Advanced cervical disease can present with torticollis, dysphagia, hoarseness, or stridor.
The differential diagnosis of patients with back pain caused by Pott's disease is extensive, and includes vascular, musculoskeletal, intra-abdominal, neurologic, renal, and autoimmune etiologies.
The diagnostic evaluation of a patient with back pain depends on the patient's history, presentation, physical examination, comorbid illnesses, and risk for serious underlying pathology. Symptoms of spinal cord compression need to be evaluated expeditiously. No imaging modality delineates findings that are pathognomonic for Pott's disease. Radiographs can be helpful, but findings of Pott's often mimic other diseases. (J Bone Joint Surg Am 1996;78:288.) Radiographs of the lumbar spine can show disk or bony destruction with loss of height, new bone formation, or soft tissue inflammation. CT is a helpful imaging modality that can demonstrate the extent of bony involvement, presence of inflammation or abscess, and violation of spinal canal contents. (Clin Orthop Relat Res 2002;403:100.) MRI is best for delineating bone and soft tissue involvement.
Diagnostic confirmation of Pott's disease requires isolation of M. tuberculosis by histopathology, culture, polymerase chain reaction, or antigen testing. The presence of acid fast bacilli in a patient clinically suspected of having TB is also supportive of the diagnosis. Typically specimens of aspirate from infected bone or soft tissue are obtained operatively or during interventional radiology procedures. Serum erythrocyte sedimentation rate (ESR) is typically elevated, but is a nonspecific finding.
Pott's disease is by definition an advanced form of TB, and it requires aggressive and prompt treatment to reduce morbidity. Prior to antituberculin medications, Pott's purported a 20 percent mortality risk. Four-drug combination chemotherapy, including isoniazid, rifampin, and either pyrazinamide, streptomycin, or ethambutol, have been the mainstay of treatment for years, and should be started empirically in patients suspected of having Pott's infection until culture sensitivities are available, according to the Centers for Disease Control and Prevention. (http://bit.ly/PottsDisease.) Treatment should be individualized to each patient, and should include pharmacotherapy either alone or in combination with surgical drainage and spinal stabilization. (Spine 1997; 22: 1791.) Patients with suspected Pott's disease should be admitted to the hospital for evaluation by a spine and infectious disease specialist.
Thank you to Ronnie Shalev, MD, and Lisa Filippone, MD, for help with this case.
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