Manifestation, management and molecular analysis of candidate genes in two rare cases of thyrotoxic hypokalemic periodic paralysis.

BACKGROUND: Hypokalemic periodic paralysis as a complication of thyrotoxicosis (THypoKPP) is common in Asians but not well recognized in Western countries or pediatric patients, where most cases are due to the familial variant (FHypoKPP). Ion channel gene mutations may underlie these diseases. We describe the first pediatric and a rare adult Caucasian case of THypoKPP in Finland.

METHODS: Manifestation and management of two THypoKPP cases. We studied for possible mutations in KCNE3, KCNJ2, SCN4A and CACNA1S genes.

RESULTS: A 15-year-old Vietnamese boy presented with sudden-onset paralysis and severe hypokalemia, 1.8 mmol/l. The case was first regarded as FHypoKPP, but thyroid function testing revealed a suppressed TSH and highly elevated FT4. A 37-year-old Caucasian male presented with acute tetraparesis. His plasma potassium was only 1.4 mmol/l. Treatment with carbimazole had been initiated two weeks earlier, but FT4 was still elevated. No mutations in KCNE3, KCNJ2, SCN4A or CACNA1S genes were detected.

CONCLUSIONS: THypoKPP is a potentially life-threatening condition which bares many similarities with FHypoKPP. THypoKPP is rare in Western countries but should be considered in sudden-onset paralysis, independently of age and especially in males. Mutations in ion channel candidate genes did not underlie the disease in the present cases.