503 - A Rare Presentation of Acute Flaccid Myelitis

Case Diagnosis: Acute Flaccid Myelitis

Case Description: An 11-year-old female who presented with 16 days of acute onset right arm weakness and pain. Two days before symptom onset, she had a febrile illness with respiratory symptoms. On initial examination, she had right upper extremity weakness, most notable proximally, and hyporeflexia. Spine MRI revealed a patchy signal abnormality within the cervical spinal cord from the cervicomedullary junction to C5 and a signal abnormality in the cord at C4-C5 more pronounced on the right. MRI of the brachial plexus was normal, and subsequent EMG revealed an acute motor process involving the right C5-C6 myotomes. Finally, a respiratory panel was positive for rhinovirus. She was treated with a course of intravenous immunoglobin (IVIG) and steroids, as well as physical and occupational therapy, with continuing improvement in strength, function, and recovery.

Discussions: Acute flaccid myelitis (AFM) is a paretic or paralytic neurologic disorder predominantly affecting children. While there is no formal diagnostic criteria for AFM, presentation typically includes a prodromal illness, following by neurological symptom onset 1-10 days after initial infection. The most common associated pathogen is enterovirus. Patients often experience pain and asymmetrical weakness, usually involving upper extremities, more proximally than distally. The hallmark radiologic finding of AFM is T2 hyperintensity of spinal cord grey matter on MRI. In early AFM, EMG findings can be limited to reduced or absent compound motor action potentials (CMAP). Additionally, CSF pleocytosis is a common finding, however not a requirement for diagnosis.

Conclusions: In conclusion, the patient’s clinical presentation of acute onset of right arm pain and weakness preceded by an atypical viral respiratory illness, along with correlating MRI and EMG findings, highlights key features consistent with acute flaccid myelitis (AFM). Treatment with IVIG, steroids, and rehabilitative therapies resulted in continued improvement underlining the importance of early diagnosis and treatment.