A 15-year-old previously healthy female was referred by dermatology for widespread itching refractory to multiple dermatologic treatments. Careful history suggested the itching sensations may have a neuropathic quality similar to paresthesias. As a pain physician comfortable with neuropathic medications, the referring physician would like you to consider a trial of gabapentin related to a possible small fiber neuropathy. On follow up, the patient reports >50% improvement in itching with low doses of gabapentin. As this is the first treatment to reduce symptoms, her mother would like to know why it helped when other treatments failed and whether she has a small fiber neuropathy.


A lab evaluation was performed and was notable for a low vitamin B12 of 170 (normal 232-1245 pg/mL). The patient denies other symptoms and there are no red flag symptoms for cancers, fatigue, or other chronic systemic diseases. The remainder of the small fiber neuropathy lab investigation is normal, including no signs of anemia, normal inflammatory levels, normal folic acid and other micronutrients, and normal thyroid studies.


What is the next best step in management?