LAUSR

Dear Editor, Tumoral calcium pyrophosphate dihydrate (CPPD) is a rare variant of crystal deposition disease. This deposition can be found intra-articular or at the periarticular structures. Intra-articular tumoral CPPD involving the metatarsophalangeal, temporomandibular, hip, spine and knee joints are well described. We report a case of unusual tumoral CPPD in a systemic lupus erythematosus (SLE) patient who presented with acute calcific tendinitis of the gluteus maximus tendon. A 48-year-old woman presented with a complaint of first episode of severe acute onset left buttock pain for 3 days. She denied recent trauma, fever or pain elsewhere. She had a background medical history of SLE diagnosed 6 years ago, complicated with lupus nephritis and pulmonary hypertension. At presentation her SLE disease activity index was low. She was taking lowdose prednisolone, mycophenolate mofetil, and sildenafil. She had neither family history of crystal arthropathy nor thyroid disorders. On physical examination, there was a palpable vague mass over the inferolateral border of the left gluteal region. The mass was tender; however, the overlying skin was not warm or erythematous. The active and passive range of movement of her left hip was full. There was no tophus or other ectopic calcinosis noted. With these, the differential diagnoses of cartilage tumor, osseous tumor, myositis ossificans or acute calcific tendinitis were made. Hospital admission was arranged for the purpose of investigations and pain relief. Laboratory investigations showed mildly elevated inflammatory markers (erythrocyte sedimentation rate 28 mm/h, high-sensitivity Creactive protein 0.84 mg/dL [< 0.3 mg/dL]) and phosphate 5 mg/dL (2.5–4.5 mg/dL). Total white cells, serum corrected calcium, parathyroid hormone by radioimmunoassay, magnesium, alkaline phosphatase, thyroid-stimulating hormone and ferritin were normal. Plain X-ray of the left femur (lateral view) showed an amorphous calcified mass posterior to the proximal femur (Fig. 1). A musculoskeletal ultrasound examination of the left gluteal region revealed a hyperechoic solid lesion with posterior acoustic shadowing at the posterolateral part of the proximal femur. Computed tomography scan showed a lobulated calcification, approximately 20 mm 9 13 mm 9 10 mm abutting upon the lateral aspect of the femur at the proximal insertion of the gluteus maximus muscle. Fine needle aspiration (FNA) under ultrasound guidance was done. The material obtained showed rhomboidal-shaped, positive birefringent crystals under polarized microscope examination, which was compatible with CPPD (Fig. 2). Under the impression of acute calcific tendinitis of the gluteus maximus secondary to CPPD, intra-lesion needle aspiration with corticosteroid and lidocaine injection was given. The pain scores reduced significantly from 5/ 10 on admission to 1/10 upon discharged. Serial followup in out-patient clinic manifested a complete resolution of pain within 2 months. Calcific tendinitis commonly occurs in patients between 30 and 60 years old, slightly more in women. The shoulders are the most common site affected even though it happens occasionally in hip, elbow, wrist and knee. Traditionally the culprit is believed to be calcium hydroxyapatite crystals deposition as these areas are relatively avascularized. Atypical site of calcific tendinitis in this case may be confused with other diagnoses such as malignancies, therefore, FNA of soft tissue was done under ultrasound guidance, interestingly revealing CPPD crystals. CPPD is associated with many medical conditions, albeit the majority are idiopathic. Our patient was screened for associated metabolic diseases such as hemochromatosis, hyperparathyroidism, hypophosphatemia, hypomagnesemia and hypothyroidism that