Thyrotoxic normokalemic periodic paralysis: a case report
Ayten Oguz1, Fevzi Balkan1, Husniye Baser1, Fikri Ak2, Reyhan Ersoy1 & Bekir Cakir1
Introduction: Hypokalemic periodic paralysis associated with hyperthyroidism is a well-known acute electrolyte and acute muscle disorder. Lesser known is normokalemic periodic paralysis associated with hyperthyroidism (TNPP). Because plasma potassium is normal, and it can be misdiagnosed as some other disorder if thyroid function is not evaluated. We report a case of TNPP due to non-autoimmune thyroiditis.
Case report: A 23-year-old woman was admitted to emergency department with muscular weakness of the lower extremities. She also presented to weight loss, increased appetite, and heat intolerance for the last 2 months. She denied any previous disease history or medication. In physical examination, her thyroid gland was minimal enlarged diffusely and non tender. In neurologic examination, there was symmetric flaccid paralysis with areflexia and impaired sensation in the lower extremities. Fasciculations, myoclonus and muscular atrophy were not observed. Cranial nerves were intact. ENMG and cranial MR were normal. Lumbar puncture was applied. Cerebrospinal fluids pressure and other related studies were normal. Laboratory studies revealed normal renal and hepatic function. Serum potassium 4.6 mmol/l (3.65 mmol/l) was. The thyroid function tests revealed a decreased level of TSH, an elevated level of fT4, and fT3. The thyroglobuline antibody and microsomal antibody test were negative. Thyroid ultrasonography revealed chronic thyroiditis. I-131 uptake was 2% in 4 h (normal: 1525%), and 1% in 24 h (normal: 2535%). The diagnosis was non-autoimmune thyroiditis accompanied by TNPP. Propranolol at a dose 20 mg four times per day was given to control of symptoms of hyperthyroidism. The paralysis completely improved without potassium supplementation.
Conclusion: Periodic paralysis can present with initial symptoms of thyrotoxicosis associated with normokalemia. Thyroid function should be evaluated in patients presenting with muscle weakness, normal potassium concentrations and thyrotoxic symptoms to avoid inappropriate management and missing a curable form of paralysis.