A CASE OF HYPOTHYROIDISM ASSOCIATED WITH IMMUNOGLOBULIN-LINKED MACRO CREATINE KINASE

Abstract

A case of hypothyroidism associated with increased serum creatine kinase due to immunoglobulin-linked macro-creatine kinase is reported. A 50 year-old woman who had been followed at our outpatient clinic because of hypertension, and treated with nilvadipine at a dose of 8 mg/day, complained of muscle weakness in her upper extremities which had persisted for a month. Laboratory examination revealed high serum creatine kinase (CK) and she was admitted for further evaluation. Physical examination showed muscle weakness in her upper and lower extremities, rough dry skin, thin hair, and non-pitting edema in her lower extremities. Isozyme analysis showed 98.5% of CK activity to be of MM type and an extra band was detected on electrophoresis of CK. Thin-layer geifiltration disclosed a normal spot and a high molecular spot. Finally, the enzyme immunofixation method revealed immunoglobulin linked CK with heavy chain; A and light chain; κ and λ . Based on physical examination findings, hypothyroidism was suspected and thyroid hormones were measured. Both free T³ and T⁴ were below the detection limit of the assay, whereas TSH was extremely high. Supplementation with levothyroxine sodium was started and her muscle weakness improved, serum CK normalized and immunoglobulin-linked CK disappeared during the course of treatment. Cases of hypothyroidism associated with immunoglobulin-linked CK are rare, only 2 cases have been reported to date in Japan.