Unexplained hip pain: look beyond the obvious abnormality.

Case history A 53 year old self employed white business man was seen by the rheumatology unit at this hospital for the first time in May 1997. Over the last three years he had seen three diVerent rheumatologists with an assymetrical arthritis, aVecting mainly the right hand. This had been diagnosed as rheumatoid arthritis, based on the presence of rheumatoid factor in the blood and treated with 10 to 15 mg prednisolone a day for the last two years, as well as periods of treatment with sulphasalazine and methotrexate in the past. He presented with a painful right thumb and a painful restriction of left hip joint movement, which had gradually increased over the previous six weeks. His past history included a four year history of pustular psoriasis without apparent joint involvement and a history of low back and left groin pain 10 years ago, investigated elsewhere with a bone scan, plain radiography, and computed tomography of the left hip, with no cause found for the hip pain. Examination revealed a well looking, afebrile man. He had obvious psoriasis on the feet with involvement of the toenails, no evidence of any deformities or active synovitis but had a painful right thumb carpometacarpal joint with crepitus on movement. Examination of his left hip joint revealed a non-pulsatile fullness in the left groin and painful restriction of left hip joint movements particularly flexion, abduction and external rotation, with virtually no internal rotation. There was no evidence of an inguinal hernia. The right hip joint had essentially full, pain free range of movement. His C reactive protein measurement was within normal limits, the rheumatoid factor was increased at 405 IU/ml (normal < 21) but radiography of the hands and feet did not show any erosive changes consistent with the diagnosis of either rheumatoid or psoriatic arthritis. He had a normal erythrocyte sedimentation rate and a blood neutrophilia (white cell count 13.1 × 10, 72% neutrophils), which was presumed to result from his corticosteroid treatment. A plain radiograph of the left hip was normal (fig 1A) but an ultrasound displayed an enlarged iliopsoas bursa containing semi-solid material, with no abnormality in the left hip joint. The iliopsoas bursa was confirmed by computed tomography of the left hip, performed on the same day as the plain radiography (fig 1B) and was aspirated under computed tomographic guidance, showing a blood stained inflammatory synovial fluid without any crystals or organisms seen or any growth on culture. Subsequent cultures forMycobacterium tuberculosis were negative. The iliopsoas bursa was injected one week later under ultrasound guidance with 40 mg Celestone Chronodose (Schering-Plough, BaulkhamHills,New SouthWales) with temporary improvement, lasting one week, in his left hip pain and restricted movements and the prednisolone dose was gradually tapered oV. His left hip continued to be painful with restricted movements and he was considerably impaired in his ability to conduct his private business. A repeat ultrasound one month after initial presentation demonstrated reduction in the size of the iliopsoas bursa to half the original size and the iliopsoas bursa was aspirated and injected again with corticosteroids. Culture of the bursal fluid again revealed no growth and he had two days of improvement in left hip pain after the second injection of the iliopsoas bursa. In view of the discrepancy between the radiological response of the iliopsoas bursa and the lack of clinical improvement in left hip symptoms, magnetic resonance imaging was performed of both hips, twomonths after initial presentation (fig 1C and D). The symptomatic left hip demonstrated a high grade avascular necrosis with some early collapse of the femoral head, while the asymptomatic right hip showed a low grade avascular necrosis. The patient is awaiting a core decompression of his right femoral head and will undergo a total hip replacement of the left hip joint after that procedure. His blood lipid profile was checked and found to be in the normal range. After withdrawal of his corticosteroids, he developed an assymetrical polyarthritis with sausage digits, typical of psoriatic arthritis and has now started oral methotrexate treatment.