ODP564 Hypercalcemia in the Setting of HTLV-1 Infection and Normal PTHrP Levels
Authors: Haridas Keerthana , Shah Nirali 
Published: November 2022

Abstract

A 53 year old male with history of HTLV-1 infection associated myelopathy but with unknown mode of transmission, presented with acute on chronic bilateral lower extremity weakness and numbness with no other deficits. Examination revealed decreased strength (grade 1/5) in lower extremities with normal bulk, tone and sensations. Initial blood work revealed hypercalcemia with corrected Calcium of 16.2mg/dl(8.5-11.5), Phosphorus of 2.7mg/dl (2.5- 4.5) and Alkaline Phosphatase of 126mg/dl(20-140). Workup for hypercalcemia revealed Parathyroid hormone (PTH) level of 14pg/ml (10-65), 25 hydroxy vitamin D at 19.6 ng/ml(30-100), 1,25 dihydroxy vitamin D at 6.7pg/ml(19.9-79.3) and TSH of 1.265 microIU/ml(0.5-5). The Parathyroid hormone related protein(PTHrP) level was low at &lt; 2pmol/L while Lactate Dehydrogenase (LDH) was 433U/L(100-220). Urine calcium creatinine ratio was 0.388. Reverse Transcriptase PCR was positive for HTLV-1 but negative for HTLV-2. Smudge cells and atypical lymphocytes were noted on peripheral smear. Imaging revealed generalized lymphadenopathy with splenomegaly but no spinal cord compression. Flow cytometry showed 7.8% atypical helper T cells, positive for CD3, CD4, CD5 and CD45. Clonal T cell receptor gene rearrangements were found, suggesting an underlying T cell neoplasm. Lymph node biopsy confirmed ATLL. He received treatment with fluids, Calcitonin and Denosumab after which serum Calcium levels fell (nadir 7.7mg/dl) and then normalized. He developed another episode of hypercalcemia 5 weeks later which was treated similarly.

Discussion
Human T cell Lymphotropic Virus-1 (HTLV-1) is a retrovirus causing asymptomatic infections, symptomatic systemic disorders and adult T cell Leukemia and lymphoma(ATLL). HTLV-1 infections, whether in asymptomatic or symptomatic patients, and ATLL are rare but important causes of hypercalcemia and hypercalcemic crises. Individuals with ATLL have the highest incidence of hypercalcemia(50-70%) among all hematologic malignancies. Hypercalcemia is a poor prognostic factor and predicts lower overall survival. It is caused by increased bone resorption, mediated by various factors with the largest role being played by Receptor Activator of Nuclear Factor Kappa B ligand (RANKL), followed by PTHrP, Interleukins, Macrophage Inflammatory Protein 1 alpha and gp 46. RANKL expression is increased upon transactivation by the viral TAX gene product and mediates conversion of osteoclast precursors to mature osteoclasts engaging in bone resorption. PTHrP expression is variable among patients, relating to levels of the TAX gene product that transactivates the PTHrP gene promoter. Thus, a low level, like in our patient, does not rule out HTLV infection as the cause of hypercalcemia. Management of hypercalcemia is in keeping with guidelines for management of other causes of hypercalcemia but may be better responsive to monoclonal antibodies against RANKL than bisphosphonates given the role of the ligand in mediating hypercalcemia in these cases. It can also be used in the setting of poor renal function, which is commonly encountered in hypercalcemic patients.
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