Non-osseous uptake on Tc99m methylene diphosphonate in multiple muscles confirmed on SPECT/computed tomography
A 55-year-old female presented to the physician with complaints of pain in the left hip radiating to the left lower limb since 1 year, gradually increased to unbearable leading to inability in walking since 1 month. She was a known case of rheumatoid arthritis since 2004, under treatment on phenylbutazone and steroids. On physical examination, we noted mild tenderness in anterior thigh muscles of left lower limb, restriction of movements in the left lower limb. No significant joint deformities. Blood investigations and biochemistry revealed hemoglobin of 12.9 g/100 ml, white blood cell: 23,000, erythrocyte sedimaentation rate (ESR): 44 mm/h (0-20), lactate dehydrogenase LDH: 521 mU/ml (100-190), serum creatine: 0.7 mg% (0.6-1.3), serum phosphate: 7.0 (2.5-4.5), uric acid: 18.9 (2.6-7.2), creatinine phosphokinase CPK: 6592 mU/ml (21-232), serum calcium: 8.9 (8.8-10.5). CT abdomen and pelvis revealed bony destruction of pubic symphysis with associated soft-tissue component suspicious of infective or metastatic etiology, diffuse osteoporotic changes, and insufficiency fracture of sacrum. Magnetic resonance imaging Lumbo-sacral spine performed later revealed altered bone marrow signal in sacral 1-3 vertebrae, grade 1 forward spondylolisthesis L5 over S1, degenerative spondylitic and disc changes with facet joint involvement of L4/L5 vertebrae. Subsequently, patient was referred for a bone scan to look for bone metastases. Whole body bone scan with 25 mCi of Tc-99m MDP was performed, which revealed multiple skeletal metastases []. In addition, extraosseous soft-tissue uptake was seen involving multiple muscles. We performed SPECT-CT images to precisely delineate the muscle involved, i.e., right adductor magnus muscle, left rectus femoris muscle and right gastrocnemius muscle. We noted calcification on CT images in right adductor magnus muscle at site of Tc-99m MDP uptake, no definite calcification was note in the left rectus femoris muscle and right gastrocnemius muscle. Subsequently, biopsy was performed from left rectus femoris muscle, which mentioned suspicion of adenocarcimatous cells. Left rectus femoris muscle did not show visible calcification radiologically (CT images) however, abnormal micro calcification was shown in muscle biopsy evaluation by electron microscopy. Myeloma profile was negative. Thus, the final diagnosis was multiple skeletal metastasis with metastatic calcification in multiple muscle from an unknown primary.