Skeletal tuberculosis mimicking seronegative spondyloarthropathy.

Sir, There has been a resurgence of tuberculosis worldwide. Approximately 10-11% of extra-pulmonary tuberculosis involves joints and bones, which is approximately 1-3% of all TB cases.1 A high degree of sensitivity to this diagnosis would permit prompt institution of anti-TB therapy and prevent irreversible joint damage. A 30 years female, presented with complaints of low backache of 2 month duration, with pain in the buttocks radiating to legs, aggravated on walking along with morning stiffness of 15 minutes duration. There was no other history of pain in any other joints, or any other neurological symptoms. She was evaluated and treated in a different hospital in 2004. X-ray lumbo-sacral (LS) and sacroiliac joint (SI joint) showed haziness of SI joint space. MRI of LS spine and SI joint (done in July 2004) showed irregular margin on right side with bone edema on left side along with altered signal intensity (Fig. 1). Patient was diagnosed as seronegative spondyloarthropathy and was started on anti-inflammatory drugs. She was admitted with us after 5 months with persistent low backache and pain in the legs and heel along with fever of 4 months duration along with significant weight loss. On examination, she was pale and febrile; there was tenderness in SI joints on both sides on applying pressure. Spine extension and flexion were painful. Investigations revealed anaemia with raised CRP, Mantoux test was positive, rest of the investigations including chest X-ray were normal. CT scan of the sacroiliac joints showed marked destruction of articular surfaces of SI joint on left side and reduced joint space on right side (Fig. 2). CT guided aspiration (Fig. 3) revealed acid fast bacilli. Patient was started on anti-tubercular treatment. After 6 months of follow up patient is better clinically and radiologically. Skeletal tuberculosis (TB) is still a common problem in developing countries. Infections of the sacroiliac joint are uncommon and the diagnosis is usually delayed.2 The sacroiliac joint is involved in 3-9.7%. Lack of awareness of this now uncommon form of infection often leads to diagnostic delay and increased morbidity.3 TB of the sacroiliac joint is usually unilateral and clinically presents with pain in the buttock and low back that may be of short duration—or as long as >1 year. There may be difficulty in clinically distinguishing it from inflammatory back pain. Other infective cause which may be sought as a differential diagnosis is Brucellosis. Features differentiating tuberculosis with brucellosis are shown in Table 1. MRI is reported to be the best modality for early detection of spondylitis. Radiographically, the sacroiliac joint may be normal or haziness or loss of the joint line may be seen in early disease. Irregularity of the articular surface and the sub-chondral erosions may follow. MR imaging is the most sensitive and specific imaging modality for diagnosing sacroiliitis at its early stage. However, because of the overlapping clinical