Diagnostic Overshadowing in Functional Neurological Disorder Leading to a Diagnosis of Acute Motor and Sensory Axonal Neuropathy: A Case Report

Background: Features intersecting neurological and psychiatric disorders impose differential diagnostic challenges, especially in younger, healthy patients. Cognitive biases, such as diagnostic overshadowing, can lead to errors for patients with neurologic deficits in the presence of psychiatric comorbidities. Methods: This case report describes a 22-year-old female patient admitted for acute inpatient rehabilitation with an initial primary diagnosis of Functional Neurologic Disorder (FND), who subsequently underwent additional neurologic work-up following clinical and functional inconsistencies. Results: Physical exam findings, lack of response to therapeutic modalities, and electromyography/nerve conduction study findings led to a full neurological work-up consistent with Acute Motor and Sensory Axonal Neuropathy (AMSAN), treated with intravenous immunoglobulin. Conclusions: Systemic peripheral neuropathies must be addressed during differential diagnosis in suspected FND, a potential gap in current practice. This report emphasizes the essential role of physiatry and the value of an unbiased, patient-centered approach, integrating clinical knowledge and compassion to ensure accurate diagnosis and appropriate treatment.