Individuals may have neurologic manifestations without anemia. Hematocrit and /or mean cell volume (MCV) can be normal in vitamin B12 deficient patients. ^9-14,22,23 Some people have vague neurologic symptoms for years prior to diagnosis of vitamin B12 deficiency. ⁹

     Of untreated patients, 80 to 90% develop disorders of the nervous system. ²⁴ Most neurologic deficits such as ataxia and dementia will resolve if treatment is initiated within 3 to 6 months after onset of dysfunction. ²⁴

     A study of B12 deficient patients with cognitive dysfunction for less than 12 months showed striking improvement with B12 therapy. However, vitamin B12 deficient patients with dementia for greater than 12 months exhibited little improvement with B12 replacement. ²⁵