Methotrexate-induced iatrogenic immunodeficiency-associated lymphoproliferative disorder causing hypercalcaemia

Hypercalcaemia is a rare but potentially life-threatening consequence of malignancies. Solid cancers, such as lymphomas, increase serum calcium primarily through parathyroid hormone-related protein or ectopic production of 1alpha-hydroxylase. We present a case of 56-year-old woman with Sjogren's syndrome and psoriasis in the setting of chronic methotrexate (MTX) use who developed worsening hypercalcaemia and symptoms suggestive of lymphoma. Pathology results diagnosed her with MTX-induced iatrogenic immunodeficiency-associated lymphoproliferative disorder (LPD). This case reminds clinicians that chronic MTX use is associated with LPDs and can ultimately lead to hypercalcaemia. The patient's MTX and other immunosuppressive medications were stopped, and her calcium corrected with fluids and calcitonin. At her 8-month follow-up postdischarge, the patient was asymptomatic with normal laboratory results and in partial clinical remission.