(Kiosk 3) An Atypical Presentation of Congenital Folate Deficiency Causing Isolated Distal Predominant Motor Neuropathy

Case Diagnosis: Congenital Folate Deficiency Causing Isolated Distal Predominant Motor Neuropathy

Case Description or Program Description: A 33 yo male with a PMHx of congenital folic acid deficiency presented with paresthesia’s, weakness, fatigue, and cramping in his bilateral lower extremities (BLE). He had been receiving leucovorin injections since childhood but had missed several injections lately and developed bilateral foot drop with a steppage gait. Physical exam showed a positive Romberg Sign, atrophy of distal leg muscles with high arches, and diffuse weakness throughout his BLE. Ankle plantar and dorsiflexion strength was 2/5. Sensation was intact. Reflexes were 2+ throughout the LE. Hoffman’s and Babinski sign were present bilaterally. Gait analysis showed a wide based gait with short stride length.

Setting: Outpatient Physiatry Clinic

Assessment/Results: Labs showed low folate ( < 1.0 ng/mL) and normal Vitamin B12 levels (373 pg/mL). MRI of the spine did not reveal any pathology. Genetic testing for hereditary motor neuropathy disorders and a heavy metals screen were negative. Nerve conduction studies revealed intact sensory function bilaterally in the sural and superficial peroneal nerves. There was no motor response when examining the bilateral tibial and peroneal nerves. EMG studies showed fibrillations with increased amplitude and duration in the bilateral tibial anterior, medial gastrocnemius, and right 1st dorsal interosseous nerves. Fasciculations in the right medial gastrocnemius and 1st dorsal interosseous nerves were noted.

Discussion (relevance): Electrodiagnostic findings show evidence of B LE neuropathy with motor predominance and sensory sparing consistent with motor neuron or anterior horn cell disease. Classic folate deficiency does not present with sensory impairment like a B12 deficiency would. After resuming leucovorin treatment folate levels normalized and symptoms drastically improved, which supports a folate deficiency as the etiology of his symptoms.

Conclusions: This case demonstrates an atypical presentation of folate deficiency causing clinically significant motor and sensory deficits despite only having electrodiagnostic findings of an isolated motor neuropathy.