Electrodiagnostic / Neuromuscular Medicine
Acute Motor Axonal Neuropathy Misdiagnosed as Functional Neurologic Disorder: A Case Report
Halle Berg, BS
Medical Student
University of Washington School of Medicine
Clarkston, Washington, United States
Conor Linehan, MD
PM&R PGY-3
University of Washington
Seattle, Washington, United States
Aaron Bunnell, MD
Associate Professor
University of Washington
Seattle, Washington, United States
Ovuokerie Addoh, MD, PhD
Asst. Professor
University of Washington
Seattle, Washington, United States
Halle Berg, BS
University of Washington School of Medicine
Clarkston, Washington, United States
A 63-year-old patient with acute onset upper and lower extremity weakness. Initial diagnosis with first presentation was functional neurologic disorder (FND) based on non-specific findings and the apparent incongruity between symptoms, neurologic signs, and initial workup. The patient’s comorbid diagnosis of schizoaffective disorder likely played a role in this first determination.
Case Description:
Re-presentation with continued weakness followed by EMG was notable for reduced amplitude of left median, ulnar, fibular, and tibial compound muscle action potentials, increased distal motor latencies, and reduced motor and sural nerve conduction velocities. These EMG findings were consistent with a diagnosis of acute motor axonal neuropathy (AMAN), a sub-type of Guillan-Barre Syndrome. They received IVIg at that time with minimal improvement in symptoms. Comorbidities including psychiatric history, social factors, and delay of appropriate therapy complicated the patient’s recovery, with eventual placement in inpatient rehabilitation four months after initial presentation. The patient’s upper extremity weakness continued to persist though gradual improvement in lower extremity weakness was noted.
Discussions:
AMAN and FND are neurologic impairments that can include motor weakness with unclear trigger and negative routine neurologic workup. Other variants of GBS can display sensory deficits as well, like FND. However, the AMAN variant is specific to motor deficits. While FND arises from a dysfunction in brain networks, AMAN is an autoimmune process leading to motor nerve destruction. Precipitating life stressors are more common in FND, while infectious triggers are more common in AMAN. This case especially highlights the importance of psychosocial equity in vulnerable populations. Misdiagnosis can delay life-saving treatments and adversely affect prognosis.
Conclusions:
In conclusion, a high index of suspicion for atypical variants of GBS is crucial for patients presenting with acute flaccid paralysis. EMG is an important component of the extensive work up that should be considered in patients with suspected FND.
