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Título

SPINAL MUSCULAR ATROPHY TYPE II WITH NEUROMYOTONIA: A CASE REPORT

Apresentação do caso único

A.F.S.S., female, 18 years old, with no perinatal complications, presented with weakness in her legs before the age of 1, acquiring gait at the age of 2 with bilateral support, hip instability when walking, and frequent falls. At the age of 7, she developed clubfoot and, at the age of 10, worsening weakness in the lower limbs when walking, associated with dyspnea, requiring a wheelchair. At the age of 14, she was seen in neuropediatrics and we found tongue fasciculations, predominantly distal hypotrophy of the lower limbs, global hypotonia, hypoactive reflexes in the upper limbs and abolished reflexes in the lower limbs, as well as trunk flexion and eyelid contraction. Normal echocardiogram, electroencephalogram and MRI of the brain in 2019, and creatine phosphokinase of 602 mg/dL. Electroneuromyography in 2019, compatible with diffuse neuromyotonia in all four limbs. No myotonic phenomena were observed clinically, but carbamazepine 400 mg/day was started as a symptomatic for neuromyotonia with partial improvement in trunk extension and eye opening. The MLPA panel of SMN1 and SMN2 showed a homozygous deletion in exon 7 of SMN1, and as the symptoms started before 18 months of age, she was diagnosed with spinal muscular atrophy (SMA) type II. Treatment with Risdiplam (6.6mL - 5mg/day) was started in 2023.

Discussão

SMA linked to chromosome 5 (SMA-5q) is an autosomal recessive disease due to a mutation in the survival motor neuron 1 (SMN1) gene, located in the 5q13 region. It is characterized by the degeneration of lower motor neurons in the spinal cord and brainstem, causing muscle weakness, which can lead to severe motor and respiratory deficits. Despite having acquired walking and subsequently losing this ability, our patient was diagnosed with SMA type II because she had motor deficits before she was 18 months old. Fasciculations may be a sign of degeneration of lower motor neuron, and it may be generated at any point of hyperexcitability.

Comentários finais

We emphasize that SMA-5q with clinical and electroneuromyographic findings of neuromyotonia is a possibility, and as far as we have reviewed, it has only been described once in the literature in Turkey. Our case did not develop other immunological or paraneoplastic diseases, confirming this atypical finding of neuromyotonia in a patient with SMA.

Referências

Zanoteli, E., et al. Consensus from the Brazilian Academy of Neurology for the diagnosis, genetic counseling, and use of disease-modifying therapies in 5q spinal muscular atrophy. Arq Neuropsiquiatr 2024; 82(01).
Koç, I., et al. A case of Isaacs’ syndrome associated with spinal muscular atrophy. Acta Neurologica Belgica, novembro/2020.
Lance, J. W. Association of lower motor neuron disorders with fasciculation, neuromyotonia and myoclonus. Aust Paediatr J, 1988:24 Suppl 1:113-5.
Pires, M., et al. Spinal muscular atrophy: descriptive analysis of a case series. Acta Médica Portuguesa, 2011; 24(S2):95-102.

Palavras Chave

SPINAL MUSCLE ATROPHY; NEUROMYOTONIA; FASCICULATIONS