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Endocrine Abstracts (2014) 35 P724 | DOI: 10.1530/endoabs.35.P724

1Hospital Clinico San Carlos, Madrid, Spain, 2Hospital Clinico Universitario de Valladolid, Valladolid, Spain.


Introduction: Fatal insomnia is a neurodegenerative spongiform prion disease. Presentation can be sporadic or hereditary (autonomal dominant). The latter, FFI, is caused by a mutation in the human prion protein gene on chromosome 20. Affected individuals present a disorderd sleep-wake cycle, dysautonomia and motor signs, with a predominance of lesions in the thalamus. SIADH has been described in two affected patients.

Case Study: A 70-year-old woman was referred to Endocrinology in July 2013 for the study of hyponatremia, following detection of a serum sodium level (SNa) of 124 mmol/l three weeks earlier, that did not respond to poorly-tolerated fluid restriction. The patient started with nocturnal insomnia in March 2013. In June she started presenting severe diurnal hypersomnia that interfered with her normal activites. Neurological diagnosis was: FFI (D-178-N mutation with methionine–methionine polymorhphism in codon 129) with hypersomnia (present in up to 50% of cases). She presented an altered gait, and mood swings. Previously diagnosed of depression, she had been on Trazadone and benzodiazepìnes for 2 years, without prior hyponatremia. Family history: one sister and three first-degree cousins had died with the diagnosis of FFI. Physical examination: euvolemia, bradypsychia, altered gait, and hyperreflexia. SNa: 129 mmol/l, urine sodium:135 mmol/l, plasma osmolality(Osm):269 mOsm/kg, urine osm:490 mOsm/kg. Normal renal, adrenal, hepatic, thyroid tests. Normal cervicothoracic CT, brain MR. Tolvaptan was initiated, attaining/maintaining eunatremia (SNa 137) with 60 mg/day. Median SNa pre-treatment:130.5 (126–132). On tolvaptan: 135.5(133 138)(P=0.018). Eunatremia was accompanied by resolution of patient’s hypersomnia, bradypsychia, with mood improvement, and normal gait. The patient resumed intellectual and leisure activities, and an active social life, drinking freely.

Conclusions: Our patient, diagnosed with the Hypersomnia form of FFI, presented resolution of hypersomnia and other symptoms following treatment of her SIADH-induced hyponatremia with tolvaptan, permitting a normal lifestyle anew. We believe that all patients with FFI and hypersomnia should be screened for hyponatremia.

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