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Magnesium/potassium Worsening of neuromuscular tetanic hyperexcitability syndrome and myopathy: case report

A 31-year-old woman developed worsening of neuromuscular tetanic hyperexcitability syndrome and myopathy, while receiving supplementation therapy with magnesium and potassium. In 2012, the woman presented to hospital of Italy with a history of recurrent muscular spasms, tetanic episodes, diffuse and persistent muscle weakness and diarrhoea. The muscular spasms were mainly localised at the hands and face, which lasted from several minutes to one hour, were often associated to tachycardia and worsened with carbohydrates ingestion and physical effort. These symptoms started in her infancy with low frequency and low intensity, but exacerbated following her first delivery and during breastfeeding. Following an initial misdiagnosis of fibromyalgia, she opted for a neurological evaluation. The neurological examination on latest presentation, revealed a mild and fluctuating weakness of iliopsoas muscles. She underwent an electromyography (EMG), that showed polyphasic motor unit potentials, suggestive for myopathic changes. The EMG tetany test resulted positive in several occasions, as after physical effort, grouped motor unit discharges appeared and persisted for over 2 minutes. Muscular spams coupled with tetanic episodes. She had mild hypocalcemia, while serum magnesium was normal. Gene sequencing showed a heterozygous mutation c.736A>G (p.Asn255Asp) in KCNA1. Of note, her magnesium excretion was normal. She received supplement-therapy with magnesium and potassium [dosages and routes not stated]. However, she developed subjective worsening of the muscular symptoms due to magnesium and potassium [time to reactions onsets not stated]. Magnesium was later discontinued. Several myorelaxants (including baclofen, cyclobenzaprine, tizanidine and unspecified benzodiazepines) and neuromodulators (including trazodone, pregabalin and amitriptyline) were administered. Calcium therapy had a slight clinical benefit on the tetanic episodes and the muscular weakness, while muscular cramps and spasms persisted. Eventually, a cerebral MRI, cardiological balance with electrocardiogram, echocardiogram and troponin level normalised. At the time of report, she was monitored on a yearly basis, and was in a stable condition. Bianchi F, et al. Neuromuscular tetanic hyperexcitability syndrome associated to a heterozygous Kv1.1 N255D mutation with normal serum magnesium levels. Acta Myologica 39: 36-39, No. 1, 2020. Available from: URL: http://doi.org/10.36185/2532-1900-007

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Reactions 22 Aug 2020 No. 1818