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Título

CONGENITAL MYOTONIA AGGRAVATED BY POTASSIUM

Apresentação do caso único

Congenital Myotonia Aggravated by Potassium (Miotonia Permanens) consists of an impairment of muscle relaxation caused by mutations in sodium channels (SCN4A) of striated muscles. Clinical characteristics vary according to age, with severe episodic neonatal laryngospasm in childhood and myotonia throughout life. Patient, female, 7 years old, started recurrent attacks of hypertonia and laryngospasm at 2 months old having been investigated for epilepsy and gastroesophageal reflux disease, excluding these diagnoses. At the age of 3, the symptoms became more frequent and were triggered by physical exertion, anxiety and infection. At age 5, in investigation at Rede Sarah, she had a genetic diagnosis- DNA panel (neuromuscular diseases) of miotonia permanens aggravated by potassium, with alteration in the gene SCN4A. In March 2024 she went to IPPMG’s emergency with contractures’ worsening during a flu-like illness that began 1 week before, using carbamazepine (8.5 mg/kg/day). The maternal report indicated exacerbation of muscle contractures and laryngospasm attacks, impossibility of walking and severe pain. On examination, the patient presented generalized contractures on the face, trunk and limbs, hypertonia and medial deviation of the hands and feet. Did not perform full extension of the upper and lower limbs. Acetazolamide was started at a dose of 500 mg/day, carbamazepine was increased to 400mg/day and started on a restricting diet of foods rich in potassium. After 6 days in intensive care unit, the patient had considerable improvement of the condition, making it possible to reduce acetazolamide to 250 mg/day. On examination, she was in good condition, had atypical gait, maintaining contractures in her fingers, reduced muscle strength in arms and fingers and normal deep reflexes in lower limbs and decreased in upper limb. Cutaneous-plantar reflex in flexion bilaterally.

Discussão

Congenital myotonia aggravated by potassium is a rare sodium channelopathy, caused by a mutation in the SCN4A gene, with autosomal dominant inheritance and high morbidity. Clinical manifestations may vary throughout life, and most of the cases present early-onset laryngospasm and intense muscle hypertonia. Depending on the phenotype presented, a good response to the use of acetazolamide is seen.

Comentários finais

There are still variations in the treatment of congenital myotonia aggravated by potassium, and some patients with partial response to carbamazepine can benefit from the use of acetazolamide.

Referências

1-DUPRÉ, Nicolas; , CHRESTIAN, Nicolas et al. Clinical, electrophysiologic, and genetic study of non-dystrophic myotonia in French-Canadians Neuromuscular Disorders , Quebec City, QC, Canada, 19 (2009) 330–334, January 2008. Disponível em: www.elsevier.com/locate/nmd;

2- HORN-LEHMANN, Frank; D’AMICO, Adele et al. Myotonia permanens with Nav1.4-G1306E displays varied phenotypes during course of life Frank,Germany, Acta Myologica • 2017; XXXVI: p. 125-134.

Palavras Chave

Congenital myotonia; Miotonia Permanens; Sodium Channelopathy