Variant, Motor Neuron Disease, and Parkinsonism: Fortuitous Association or a Potentially Underestimated Pathophysiological Mechanism?

A 72-year-old Brazilian woman presented with a 4-year history of rest tremors of the hands, followed by slowness of movement, and a diagnosis of idiopathic Parkinson's disease. She was started on dopamine agonists with significant improvement. After three years, she complained about slowly progressive dysphagia, dysphonia, quadriparesis, and cramps and fasciculations. A neurological examination disclosed distal-dominant quadriparesis, dysarthria, atrophy and fasciculation of the tongue, global brisk tendon reflexes, fasciculations, bilateral ankle clonus, and moderate spasticity of the lower limbs. She had also palpitations, dyspnea, and one episode of paroxysmal atrial fibrillation. Electrocardiography revealed a short PR interval, a widened QRS complex, and the delta wave, suggestive of Wolff-Parkinson-White syndrome. Brain and spine MR imaging, a cerebrospinal fluid analysis, and general serum lab exams were unremarkable. Needle electromyography disclosed chronic denervation involving cervical, thoracic, lumbosacral, and bulbar levels associated with acute denervation, including positive sharp waves, fasciculations, and fibrillation potentials. This patient fulfilled the diagnostic criteria for amyotrophic lateral sclerosis associated with parkinsonism. A broad next-generation sequencing-based panel disclosed the presence of the novel heterozygous variant c.1247C > T (p.Pro416Leu) in the gene (NM_016203.4). Clinicians must be aware of the possibility of variants in complex clinical scenarios associating cardiac arrhythmia, preexcitation syndromes, hypertrophic cardiomyopathy, motor neuron disease, and parkinsonism.