"Whippets"-induced vitamin B12 deficiency and dorsal column degeneration

A 32 year old pregnant woman at 11th week gestation presented with 2 weeks of progressive gait difficulty and ascending weakness. Patient admitted to recreational inhalation of nitrous oxide from whipped-cream bulbs "whippets". On examination, she had mild weakness in her extremities. Laboratory examination was significant for a low serum cobalamin (vitamin B12) level. Furthermore, homocysteine and methylmalonic acid were elevated. Parietal cell and intrinsic factor antibodies were negative. She was started on vitamin B12 injections and transferred to an acute rehabilitation facility