MEDULLARY THYROID CARCINOMA PRESENTING WITH SEVERE HYPOKALEMIA

Document Type

Conference Proceeding

Publication Date

3-20-2024

Publication Title

Am J Kidney Dis

Abstract

Medullary thyroid carcinoma (MTC) accounts for about 5-7% of all thyroid malignancies. Most MTC are sporadic in nature. The age at initial presentation ranges between 41 and 55 years. Aside from signs and symptoms of Cushing's disease, other clinical features included weakness, exertional dyspnea, galactorrhea, back or hip pain and pathological fractures. 38 year old male presented to the hospital due to left upper extremity swelling and redness. On arrival, labs were significant for hypokalemia, 2.6 mmol/L and hyperglycemia at 166 mg/dL. He was diagnosed with acute cellulitis and started on antibiotics. Replacement of potassium resulted in minimal improvement and recurrence of severe hypokalemia prompting further work up. Urine electrolyte panel results were suggestive of renal potassium wasting defect. Aldosterone level was 5 ng/dL and direct renin level was 9.4 pg/ml. Random cortsiol level was high. Dexamethasone suppression test showed elevated cortisol levels confirming ectopic ACTH. Brain MRI revealed no pituitary lesions. Due to lack of improvement in the left arm swelling, patient underwent CT scan for possible obstruction. It showed mass in the thyroid region with abdominal lymph nodes, and multiple hepatic lesion. Liver biopsy was done which was consistent with medullary thyroid carcinoma. Patient was started on metyrapone with improvement of cortisol levels. Patient was then started on Selpercatinib, with follow up with heme/onc, nephrology, and endocrinology. Currently, patient's potassium is well controlled. The diagnosis of ectopic ACTH production secondary to MTC is based on the presence of hypercortisolism not suppressed by high cortisol, absence of pituitary adenoma, and Cushing syndrome symptom. Treatment for ACTH production include adrenolytic. In extreme cases bilateral adrenolectomy may be needed. Tyrosine kinase inhibitors including selpercatinib, and vandetanib are used for chemotherapy for MTC. Immunotherapy was found to significantly decrease cortisol and ACTH levels. Other substances associated with MTC include production of corticotrophin-releasing factor and serotonin, occurring typically in distant metastases. Ectopic ACTH must be considered in the differential diagnosis in the setting of thyroid neoplasm, while investigating for severe refractory hypokalemia.

Volume

83

Issue

4

First Page

S64

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