Diagnosis
Tuberculosis osteomyelitis.
Discussion
The final diagnosis in this case was definitive only after the cultures for Mycobacterium tuberculosis were found to be positive weeks after an open biopsy. This case highlights the diagnostic problems that can be encountered in the western world due to atypical presentations of tuberculosis. The lesion was initially thought to be a neoplasm because of the extent of cortical destruction without involvement of the adjacent joint, inflammatory signs, or evidence of an abscess mimicking a neoplastic process within the acetabulum.
Skeletal involvement has been reported in approximately 11% of extra-pulmonary tuberculosis cases in the United States between 1999 and 2004 [1]. The most common skeletal presentation is localized pain and swelling associated with fever and weight loss over a period of months to years [2]. Although tuberculosis can affect any bone in the body, the most common location of skeletal tuberculosis is the spine (about 50% of cases) followed by the hip (10%), knee (10%), pelvis (4?12%), and the foot and ankle (6%). Only about 1% of skeletal tuberculosis cases involve the ilium and/or ischium without breakthrough into the joint space [3].
Skeletal involvement of tuberculosis in long bones usually involves the epiphyseal or metaphyseal regions and the adjacent joint thought to be due to seeding of bacterial emboli [2]. Acutely the sub-articular margin is blurred. Erosions can occur over time leading to cartilage damage and joint space narrowing. Tuberculosis can erode through the cortex and have an associated soft tissue mass as well. When the hip is involved, patients with active disease usually present with limping and pain, which may wake them up at night, whereas late presenting patients may have cold abscesses, cartilage damage, and hip deformities. Physical examination often reveals pain on active and passive movement. Pelvic involvement is generally associated with sacroiliac, hip joint, or rarely pubic symphysis involvement, but in cases in which these joints are not directly affected, atypical presentations can occur.
In the United States where skeletal tuberculosis is rare, it tends to remain low on the differential or is even omitted, especially when signs of infection are absent. Tuberculous osteomyelitis can be mistaken for a neoplasm especially if no septic joint is present, the imaging findings are atypical, and there is no history of pulmonary tuberculosis. The symptoms associated with tuberculosis such as weight loss and night sweats with the absence of high fevers are typically seen in the oncologic population as well.
This case underscores the necessity of considering a wide differential diagnosis in the diagnostic process of osteolytic lesions and of continuing to pursue the correct diagnosis in difficult cases such as this one, in which the initial biopsies and culture were non-diagnostic. To our knowledge this is the only case of tuberculosis mimicking an acetabular bone tumor to be reported in the United States within the last 53 years.
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