Multiple System Atrophy (Cerebellar Type) With Overlapping Progressive Muscular Atrophy Features and Genetic Erb-B2 Receptor Tyrosine Kinase 4 (ERBB4) Amyotrophic Lateral Sclerosis Variant: A Case Report.

Multiple system atrophy (MSA) is a progressive disease with Parkinsonism, dysautonomia, and cerebellar symptoms wherein patients can present with a broad range of confusing and overlapping findings attributable to various neuroanatomical substrates. Although possible, weakness is an unusual primary complaint, warranting further work-up for another neurodegenerative disease. The involvement of the more central structures, such as the locus coeruleus, pontine micturition center, and the cerebellum, can explain the wide range of symptoms. While Onuf's nucleus contributes to the urinary symptoms, anterior horn cells can implicate a motor neuron disease. Taking the varied neuroanatomical substrates into consideration, patients can present with a plethora of dysregulated motor symptoms. The authors share the course of a patient with clinically established MSA-cerebellar type and lower motor neuron disease findings at par with progressive muscular atrophy (PMA), but tested positive for an ERBB4 gene mutation, which is linked to an amyotrophic lateral sclerosis (ALS) variant. A 65-year-old Chinese female manifested with bilateral leg weakness and urinary incontinence. Over the next five years, she developed recurrent pre-syncopal attacks, asymmetric limb tremors, memory lapses, laughing fits, and a staccato-like voice. Medical management with anti-Parkinsonism drugs did not help her condition. Repeated annual non-contrast enhanced cranial magnetic resonance imaging (MRI) revealed gradual cerebellar atrophy, and an eventual prominent "hot-cross bun" sign. Because of episodes of orthostatic hypotension, with a systolic blood pressure as low as 50 mmHg, she gradually became bedridden with progressive arm weakness and sleep issues. These prompted her admission. Saccadic dysmetria and ataxic dysarthria aided in the diagnosis of MSA-cerebellar type, while motor neuron disease findings included tongue fasciculation, asymmetric leg atrophy, and polyminimyoclonus, suggestive of PMA. Neurophysiological studies confirmed this, while whole genome sequencing yielded an ERBB4 gene ALS variant of uncertain significance. She remained compliant with physical therapy during her admission. Although she was prescribed fludrocortisone for symptomatic relief and a two-week course of edaravone, she was discharged with minimal improvement and wheelchair-bound. However, the patient eventually expired two years afterward due to systemic complications. Although suspicion for a certain movement disorder can be initially made with physical examination, diagnostics can shed further light on the patient's pathology, exemplifying the uniqueness of this case report and how varying neurodegenerative movement disorders can coexist in a single patient.