Electrocardiographic Fasciculations as a Diagnostic Clue in a Floppy Infant - A Case Report of Spinal Muscular Atrophy

Background: Spinal muscular atrophy (SMA) is the most common cause of peripheral hypotonia. Due to variable clinical phenotype and severity of the disorder, there is often a diagnostic delay and use of unnecessary and expensive investigations. Clinical Description: A 1-year-old child, born of a nonconsanguineous marriage with an uneventful perinatal period, presented with isolated motor delay and floppiness of limbs, with onset since 6 months of age. Anthropometric parameters were normal for age, with neither facial dysmorphism nor tongue fasciculations. Neurological examination revealed axial and appendicular hypotonia with poor antigravity power and absent deep tendon reflexes, suggesting a peripheral hypotonia. Management and Outcome: Routine blood investigations and neuroimaging of the head and spine were normal. Before conducting nerve conduction tests, electromyography, and genetic analysis, an electrocardiogram (ECG) was performed, which revealed tremors along the isoelectric line. Being indicative of SMA, a less expensive targeted multiplex ligation-dependent probe amplification for survival motor neuron ( SMN ) gene was done, confirming homozygous deletion of exons 7 and 8 in SMN1 gene with three copies of SMN2 gene, suggestive of SMA type 2. Parents were counseled, and the child was provided physical rehabilitation and immunization. Conclusion: The case creates awareness regarding the typical “spikes on isoelectric line” in ECG as an important diagnostic clue for SMA so that further focused and less expensive genetic tests can be carried out in a floppy infant for confirmation of diagnosis.