Symptoms of vitamin B12

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vitamin B12 deficiency symptoms clinical features

Harrison's Principles of Internal Medicine, Twenty First Edition

Page 14215

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vitamin B12 deficiency symptoms signs

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Vitamin B12 Deficiency — Symptoms & Clinical Features

Vitamin B12 (cobalamin) deficiency presents across multiple organ systems. Here is a comprehensive breakdown:

🩸 Hematological

Megaloblastic anemia — fatigue, pallor, weakness, shortness of breath
Jaundice (mild, from ineffective erythropoiesis)
Hypersegmented neutrophils on blood smear
Elevated MCV (macrocytosis)

🧠 Neurological (Subacute Combined Degeneration)

These are the most serious manifestations and can occur even without anemia:

Peripheral neuropathy — tingling, numbness, burning in hands and feet (stocking-glove distribution)
Myelopathy — weakness, spasticity, hyperreflexia (dorsal and lateral column involvement)
Gait disorders / ataxia — unsteady walk, positive Romberg sign
Dementia / cognitive decline
Frontal lobe syndrome — behavioral and personality changes
Optic neuropathy — blurred vision, visual field defects
Olfactory dysfunction — reduced sense of smell

🫀 Cardiovascular

Elevated homocysteine → increased risk of atherosclerosis, DVT, stroke
Palpitations and dyspnea (anemia-related)

🖐️ Dermatological

Hyperpigmentation — particularly over knuckles and dorsal hands (a characteristic sign)
Hair loss

Hyperpigmentation over knuckles in B12 deficiency

Patchy facial hyperpigmentation (Panel A) and prominent knuckle hyperpigmentation (Panel B) — classic cutaneous signs of vitamin B12 deficiency / megaloblastic anemia.

🗣️ Oral / GI

Glossitis — smooth, beefy-red, sore tongue (Hunter's glossitis)
Anorexia, weight loss, constipation or diarrhea

🧒 Special Populations

Population	Notable Feature
Infants (of deficient mothers)	Developmental delay, hypotonia, failure to thrive
Pregnancy	Neural tube defects in fetus, maternal neuropathy
Elderly	Dementia may be the presenting symptom
Post-gastrectomy	Loss of intrinsic factor → absorption failure

⚠️ Key Clinical Pearl

Neurological symptoms can appear before anemia develops. A normal CBC does not rule out B12 deficiency. Always check serum B12 (and methylmalonic acid / homocysteine if borderline) in any patient with unexplained neuropathy or cognitive decline.

(Harrison's Principles of Internal Medicine, 21st Edition, p. 14215)

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