What is the treatment for paresthesias of the hands and feet due to suspected B vitamin deficiency, particularly B12 (cobalamin) deficiency?

Treatment for B12 Deficiency-Related Paresthesias

For paresthesias of the hands and feet due to suspected vitamin B12 deficiency, treatment with 1000-2000 μg of vitamin B12 daily (oral) or 1000 μg intramuscularly monthly is recommended, with treatment initiated promptly to prevent permanent neurological damage. 1

Diagnostic Approach

Before initiating treatment, confirm B12 deficiency with appropriate testing:

• Initial testing should use either total B12 (serum cobalamin) or active B12 (holotranscobalamin) 1
• Interpret results according to these thresholds:
  • Total B12 <180 ng/L or active B12 <25 pmol/L: Confirmed deficiency
  • Total B12 180-350 ng/L or active B12 25-70 pmol/L: Indeterminate
  • Total B12 >350 ng/L or active B12 >70 pmol/L: Unlikely deficiency 1
• For indeterminate results, measure serum methylmalonic acid (MMA) to confirm B12 deficiency 1
• Consider comprehensive testing including MMA, homocysteine, complete blood count, and folate levels 1

Treatment Regimens

For Confirmed B12 Deficiency:

1. Patients with normal absorption:

   • 1000-2000 μg daily oral supplementation 1

2. Patients with malabsorption conditions (ileal resection, pernicious anemia, etc.):

   • Intramuscular administration of 1000 μg monthly 1, 2
   • For pernicious anemia: Monthly injections required for life 2

3. Special populations:

   • Post-bariatric surgery: 1000 μg oral B12 daily indefinitely 1
   • Crohn's disease with ileal involvement/resection: 1000 μg monthly if >20 cm of distal ileum is resected 1
   • Vegans/vegetarians: Daily B12 supplementation of 250-350 μg or weekly 1000 μg 1

Urgency of Treatment

Early treatment is crucial as vitamin B12 deficiency left untreated for more than 3 months may cause permanent degenerative lesions of the spinal cord 1, 2. Paresthesias associated with vitamin B12 deficiency may be central (myelopathic) or peripheral (neuropathic) in origin 3, and early intervention is essential to prevent irreversible neurological damage.

Monitoring Response

• Check vitamin B12 levels after 3 months of supplementation 1
• For indeterminate B12 levels (180-350 ng/L) after treatment, measure MMA levels to confirm metabolic B12 deficiency 1
• Monitor for clinical improvement of neurological symptoms, which should begin within the first 3 months of treatment 4

Clinical Pearls and Pitfalls

• Important caveat: Folic acid supplementation may mask the hematologic manifestations of B12 deficiency while allowing neurological damage to progress. Doses of folic acid greater than 0.1 mg per day may result in hematologic remission in patients with vitamin B12 deficiency, but neurologic manifestations will not be prevented 2

• Critical point: Normal hematocrit and mean corpuscular volume do not rule out B12 deficiency. In 27.4% of cases, hematocrit may be normal, and in 23% of cases, mean corpuscular volume may be normal despite significant neurological symptoms 4

• Treatment response: All patients with neurological symptoms due to B12 deficiency should show some improvement with treatment. In approximately 47% of cases, complete recovery is possible 4

• Duration of symptoms matters: The extent of neurological recovery is strongly related to the duration of symptoms before treatment. Longer delays in diagnosis and treatment are associated with poorer outcomes 4, 5

• Individualized treatment frequency: While standard protocols recommend monthly injections for malabsorption cases, up to 50% of individuals may require more frequent administration (ranging from daily or twice weekly to every 2-4 weeks) to remain symptom-free 5