A 69-year-old man visited our department of neurology with symptomsof paresthesia on the lower extremities and lumbago. Biochemical examination of serum samples showed hypercalcemia (serum concentration 15.6 mg/dl). The levels of intact parathyroid hormone (i-PTH) and 1,25dihydroxyvitamin D were suppressed, whereas parathyroid hormone-related peptide (PTHrP) was elevated up to 5.4 pM (normal range: below 0.6 pM). Additionally, bone survey revealed a punched-out lesion in radiological examinations of the skull. Bonemarrowaspiration demonstrated manyatypical plasma cells suggesting multiple myeloma. Nephrogenouscyclic adenosine monophosphate(CAMP), urinary deoxypyridinoline, plasma interleukin 6 (IL-6) and transforming growth factor p (TGFP) concentrations were elevated, whereas %of renal tubular reabsorption of phosphate ( % TRP) was decreased. The immunohistochemical results demonstrated the expression of PTHrPin atypical plasma cells. These data indicated that hypercalcemia complicating multiple myelomacauses an elevation of renal calcium reabsorption and an increase of bone resorption mediated by PTHrP action.
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