Endocrine Abstracts

Introduction: Asymptomatic, mild or moderate elevations of creatine phosphokinase are frequently found in hypothyroidism, but rhabdomyolysis is rare, and even more so when it constitutes its clinical presentation.

Clinical case: A 26-year-old male who regularly practiced sports, with no family or personal history of interest, went to the emergency room referring to myalgia, generalized cramps, and muscular weakness in the previous two weeks which had not improved with an anti-inflammatory treatment. The symptoms appeared after resuming training, which had been suspended due to severe asthenia one month before. The physical examination was normal and in the biochemical exam, the following were observed: CPK 1.494 U/L (MB 46 U/L), aldolase 9 U/L (2–7.6), LDH 812 U/L, creatinine 1.84 mg/dl, myoglobinuria 0.38 (N<0.171), GOT 103 U/L, GPT 103 U/L, urates 7.89 mg/dl, cholesterol 293 mg/dl, calcium 10.5 mg/dl, ionic calcium 4.32 mg/dl, total proteins 9.53 g/dl and polyclonal hypergammaglobulinemia. Cortisol, serology and anticardiolipin and smooth muscle antibodies were normal. The electrocardiogram showed sinus bradycardia, the echocardiogram a minimal pericardial effusion, the thyroid ultrasonography, reduced size and glandular echogenicity and the neurophysiological study increased the latency of the F waves in nerves of the lower limbs. Severe autoimmune primary hypothyroidism was confirmed (free-T4 <0.2 ng/dL, TSH 120.65 mIU/L, antithyroglobulin and antimicrosomal antibodies >5.000 U/ml) and replacement therapy with sodium levothyroxine was initiated. A few weeks later all the analytical parameters were normalized, the pericardial effusion disappeared and the patient was asymptomatic.

Discussion: Rhabdomyolysis is an infrequent manifestation of hypothyroidism and, in most cases, such as above described, exercise, previous chronic renal failure or lipid-lowering drugs are identified as precipitating factors. A threshold myoglobinuria level related to the development of renal failure has not yet been defined. It is believed that dehydration and low urinary pH are involved in its pathogenesis since uric acid can precipitate in the distal tubule in the presence of acid urine and high levels of lactate. This could explain why alterations of the renal function appeared in this patient in spite of the moderate elevation of the muscular enzymes. Since rhabdomyolysis can become a severe medical issue when complicated by acute renal failure, it could be cost-effective to perform thyroid functional tests on all individuals who perform intense physical exercise.