Nutritional Disorders: Malabsorption, Malnutrition, Vitamin Deficiencies
Vitamin B12 (Cobalamin) Deficiency
Most common form: pernicious anemia; anemia, neurologic symptoms, atrophy of epithelial covering of tongue. Other causes: tropical sprue, gastric resection, ileal resection, jejunal diverticula.
Physiology
Animal products, sole dietary source for humans. Gastric acid needed for peptic digestion to release the vitamin from proteins. Intrinsic factor needed for absorption of B12.
Pathogenesis
About 80% of adult-onset pernicious anemia attributed to lack of gastric intrinsic factor secondary to atrophic gastritis. Presumed autoimmune disorder.
Pathology
Symmetric loss of myelin sheaths, most prominent in posterior and lateral columns (combined system disease). Thoracic cord affected first; also sensorimotor neuropathy.
Clinical Features
Neurologic symptoms or signs in 40% of patients with B12 deficiency. Age usually >60. Combined features of both myelopathy and peripheral neuropathy.
Symptoms: burning, painful or numb, tingling in hands and feet (most common symptom), sensory ataxia, memory loss, visual loss (optic neuropathy), orthostatic hypotension, anosmia, impaired taste, sphincter symptoms, impotence.
Sensory signs: glove-stocking sensory loss (especially vibratory and position sense), Romberg sign. Upper motor neuron signs: increased tone, impaired alternating movements, hyperactive tendon jerks, Babinski and Hoffmann signs. Cerebral signs: mild-to-severe dementia.
Laboratory Data
Blood levels of vitamin B12 <200 pg/mL. Serum methylmalonic acid, homocysteine increased in 99%. Severe anemia in only 20% of patients with neurologic findings.
MRI: increased T2-weighted signal and contrast enhancement of posterior and lateral columns of spinal cord. EMG: axonal or demyelinating sensorimotor neuropathy.
Treatment
B12 intramuscularly daily for first week, then weekly injections for first month, then monthly injections for life. About 50% left with some abnormality on examination; residual disability depends on duration of symptoms.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
