Last modified: 2018-09-09
Abstract
Introduction: Paramyotonia congenita (PMC) is a congenital disorder characterized by myotonia due to mutations of SCN4A. Myotonia was easily induced by exercise and cold exposure. PMC has not been said to have central nervous system symptoms, but we experienced one PMC patient with intellectual disability and epilepsy. Topiramate (TPM) and lacosamide (LCM) was effective for myotonia of this patient.
Patient: Patient is an 18-year-old japanese girl. Few days after birth, apnea and cyanosis appeared repeatedly after crying, gradually followed by local myotonia in various parts of the body. Exposure to both hot and cold, exercise, and mental stress induced myotonia several times a day. Generalized tonic-clonic seiaure had occurred on her since she was 1year 11 months old, and her FIQ of WISCⅢwas 48 at the age of 13.
We diagnosed her with PMC by detecting a c.3917G>A (p.Gly1306Glu) mutation in SCN4A. Mexiletine led to slight improvement, and TPM provided relief of myotonia into about half. But we discontinued TPM after decreased perspiration occurred as a side effect, leading to elevated body temperature and symptom exacerbation in the summer. We resumed TPM at lower dosage after myotonia made it difficult for her to walk, providing some symptomatic relief. A marked reduction in myotonia was seen after adding LCM.
Discussion: TPM enhances the rapid inactivation of sodium and calcium channels, while LCM enhances slow inactivation of the sodium channel. We think the combination of two types of sodium channel suppressors was effective in this case.