A girl aged three years and ten months was seen for recurrent episodes of muscle weakness in the lower limbs, which recovered spontaneously within minutes. Personal history of no interest. Controlled pregnancy without incident; vaginal birth. Artificial lactation. Normal perinatal and psychomotor development. No muscle weakness or cramps reported up to six months previously.
Family history included hyperkalemic paralysis in several relatives on the paternal side (father, paternal uncle and aunt, paternal grandmother) without providing further details and without being able to specify the genetic study.
The clinical picture began about six months before coming to the clinic, being previously asymptomatic; they reported 3-4 intermittent episodes, on separate days, of muscle cramps and a feeling of numbness in the lower limbs while sleeping, from which she recovered spontaneously in a few minutes. She showed no other clinical manifestations or involvement of other limbs. Since these episodes the patient remained asymptomatic.
Clinical and neurological examination was normal at the time of examination, with normal strength, sensitivity and osteotendinous reflexes.
In view of the suspicion of familial hyperkalemic paralysis, an analytical study was requested with a haemogram and biochemistry, which were normal. Blood count was normal, electrolytes in blood and urine normal, K 4.5 mEq/l with fractional potassium excretion (FEK) of 13%. It was not possible to perform blood tests coinciding with the clinical presentation.
Electromyography (EMG), creatine phosphokinase (CPK) and electrocardiogram (ECG) could not be performed at the same time as the clinical examination, as the patient had no new symptoms. The electromyography (EMG), without coinciding with the clinical picture, was normal.
In view of the clinical suspicion, given the family history, despite the fact that the clinical manifestations were not very evident, a genetic study of the SCN4A gene (OMIM +603967) was requested, detecting a heterozygous p.Thr704Met mutation.
At the time of diagnosis, treatment with oral acetazolamide was not started as the episodes of muscle weakness have not recurred and serum potassium values were normal in the controls performed. Periodic clinical and analytical controls will be carried out to assess whether, at some point, medical treatment is required. A diet not rich in potassium was prescribed.