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CASE OF GENERALIZED MYOCLONIAS CAUSED BY SEVERE HYPONATREMIA INDUCED BY TOPIRAMATE

RESUMO

Female, 73 years old, rural worker, admitted to the movement disorders clinic for investigation of generalized and progressive myoclonus since 2016 with cognitive decline, and worsening 1 year ago. The movements started in the foot or hand and spreading to the other limbs, sparing the face. It started only in the left upper and lower limbs, but progressed to the right hemibody. The myoclonias lasted up to 3 days, including during sleep, but with decreased intensity. She had type 2 diabetes mellitus and systemic arterial hypertension and was using topiramate, chlorthalidone, valsartan+hydrochlorothiazide, metformin, biperiden, acetylsalicylic acid, and simvastatin. On neurological examination, she presented bilateral tabetic gait, inability to perform tandem gait, and bilateral anarthesia. Dysmetria and decomposition in the index-nasal and index-finger in the upper limbs were also evident. Ideative and ideomotor apraxia and visuospatial dysfunction. During the investigation, severe hyponatremia (serum Na of 104) was found, and the patient became drowsy; intravenous NaCl 3% replacement was performed. The main diagnostic hypothesis was a syndrome of inadequate ADH secretion (SIADH) caused by topiramate. A liquor analysis revealed an acellular pattern, with normal glucose and protein. During the investigation of the myoclonus picture, the electroencephalogram (EEG) results were awake and drowsy without abnormalities and the magnetic resonance imaging (MRI) of the skull showed no relevant alterations. At clinic follow-up, after correction of hyponatremia and suspension of topiramate, there was improvement of movements. DISCUSSION: SIADH has many etiologies, through physiological, pathological or drug alterations. In particular, oxcarbazepine and carbamazepine act in part by increasing sensitivity to ADH. Similarly, it was observed in a control study that older patients taking the anticonvulsants valproate, phenytoin, and topiramate had an increased risk of hospitalization for hyponatremia, as observed in this case. Therefore, hyponatremia should be noted as a possible etiology of metabolic myoclonus, among others such as hepatic encephalopathy and uremia. FINAL COMMENTS: Authors describe a rare case of SIADH caused by topiramate, a drug poorly correlated as a cause of hyponatremia in the medical literature. Hyponatremia resulting from this disorder can lead to severe consequences, such as movement disorders, which incapacitate for daily activities.

Palavras Chave

SIADH; Hyponatremia; Myoclonias; Topiramate.

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