Tuberculous Spinal Infection

Introduction

Tuberculosis (TB) is classically considered an infectious disease of developing countries; however, it has made a resurgence in other areas of the world with the increased use of immunosuppressive drugs, increased immigration, and the relatively recent appearance of HIV. The musculoskeletal system is the most common extrapulmonary site of TB infection, with spinal involvement seen in 50% of skeletal cases. Tuberculous spondylitis refers to vertebral body involvement with TB. When compared with pyogenic infections of the spine, tuberculous spondylitis has a distinct pattern of spinal involvement on imaging, as well as a unique pattern of progression that warrants its own description.

Within endemic countries, tuberculous spondylitis typically affects children and young adults during primary lung infection; however, in Western countries adults are more commonly affected after reactivation of latent disease. As a result, the clinical diagnosis of early spinal TB can be difficult in patients without a known history of pulmonary TB. Less than half of these patients will have simultaneous pulmonary infection. Furthermore, the classic constitutional symptoms of TB (e.g., fever, night sweats, weight loss) are present in less than 40% of spinal cases and may not become clinically apparent for months after initial spinal involvement. The usual duration of illness ranges from 4 to 11 months. In some instances the diagnosis may be delayed by more than a year.

Most patients will seek medical care only after developing severe pain or neurologic complications. Radiologic examinations are one of the first and most important steps in establishing the diagnosis of tuberculous spondylitis. The goal of early diagnosis is avoiding significant morbidity associated with spinal instability, which may occur with delayed treatment. After suspicious imaging abnormalities are identified in the spine, percutaneous image-guided bone or soft tissue biopsies can be performed. Acid-fast staining or polymerase chain reaction can be used to quickly identify the organism when specifically suspected. Notably, TB is notoriously difficult to isolate on cultures, averaging 4 to 6 weeks to obtain results, with a sensitivity of 80%. As a result, microbiology data are often negative. Histopathology of the bone biopsy may show nonspecific granulomatous changes suggesting TB. The cryptic clinical and microbiology features of this disease accentuate the need for an accurate imaging diagnosis.

Lastly, spinal TB is far from a new disease. DNA analysis has identified TB strains from bone biopsies of ancient Egyptian mummies, making it one of the oldest known communicable diseases. However, newer multidrug resistant TB strains have been discovered, necessitating prolonged and aggressive treatment regimens.