Introduction: Primary skeletal muscle lymphomas are extremely rare, accounting for less than 1% of extra-nodal lymphomas.1 Hypercalcaemia is a common reason for admission to hospital. There are four main mechanisms by which neoplasms can cause hypercalcaemia; secretion of parathyroid hormone-related peptide, osteolytic metastases, (rarely) ectopic PTH secretion, and expression of 1 alpha hydroxylase, causing excess activated vitamin D and gastrointestinal absorption of calcium.2 We present a case of primary skeletal muscle lymphoma initially presenting with hypercalcaemia of unclear aetiology.
Case: A 78 year old female with a background of hypertension and CKD4 presented to acute medicine at the Queen Elizabeth University Hospital in an acute confusional state and was found to have a severe hypercalcaemia with an adjusted calcium of 3.90 mmol/l (ref. range 2.102.60). Serum PTH was within the reference range. CT of chest, abdomen and pelvis showed no evidence of malignancy. An isotope bone scan was unremarkable. This was treated with intravenous fluid hydration, furosemide and bisphosphanate with restoration of normocalcaemia and she was discharged with outpatient follow-up. Between outpatient visits she developed further episodes of significant hypercalcaemia (>3.0 mmol/l) which were responsive to high-dose steroids. Parathyroid subtraction scan did not demonstrate a parathyroid adenoma. 25-OH Vitamin D (the standard assay in our hospital) was normal. 1,25 OH Vitamin D was grossly elevated at 257 pmol/l. FDG PET-CT demonstrated a highly avid mass involving the left thigh and knee. Biopsy of the lesion confirmed primary B cell lymphoma of skeletal muscle.