Nutrition Diet · Supplementary · from Nutrition Diet

Case 1: Vitamin B12 Deficiency in Vegan Patient

Patient Presentation

Demographics: 34-year-old female graphic designer

Chief Complaint: "I've been feeling exhausted, my hands and feet tingle, and I keep forgetting things."

History of Present Illness: Ms. Patel adopted a strict vegan diet four years ago for ethical and environmental reasons. She has been conscientious about her diet, consuming a variety of whole grains, legumes, fruits, and vegetables. However, she has never taken a B12 supplement, stating she believed she could obtain adequate nutrition from plant sources alone. She was not aware that vitamin B12 is essentially absent from unfortified plant foods.

Over the past six months, she has developed progressive fatigue that limits her ability to work full days. She describes bilateral paresthesias in her hands and feet ("pins and needles"), which initially occurred intermittently but are now constant. She reports increasing difficulty with concentration and short-term memory, often forgetting conversations and misplacing items. Her partner has noticed she has become more irritable and emotionally labile.

She also describes a sore, smooth tongue that makes eating spicy foods painful, intermittent diarrhea, and a feeling of unsteadiness when walking in the dark. She has noticed shortness of breath with climbing two flights of stairs, which she attributed to being "out of shape." She denies heavy menstrual bleeding or other sources of blood loss.

Past Medical History:

• No significant medical history
• No surgeries (specifically no gastric surgery)
• No history of autoimmune disease

Medications:

• No prescription medications
• Occasional iron supplement (self-directed, not consistent)
• No B12 supplementation
• No fortified foods regularly consumed

Social History:

• Strict vegan for 4 years (no eggs, dairy, or any animal products)
• Graphic designer; works from home
• Non-smoker; social alcohol (wine, 1-2 glasses/week)
• Avid yoga practitioner
• No recreational drug use; no nitrous oxide exposure

Family History:

• Mother: Pernicious anemia (diagnosed at age 55)
• Father: Type 2 diabetes
• Non-contributory otherwise

Physical Examination

• Vital Signs: BP 110/68 mmHg, HR 102 bpm, RR 18, Temp 98.8°F, SpO2 97%, BMI 21.4 kg/m²
• General: Pale-appearing female; appears fatigued
• HEENT: Pale conjunctivae; icteric sclerae (mild); glossitis — smooth, beefy-red tongue with loss of papillae; angular cheilitis
• Cardiovascular: Tachycardic; systolic flow murmur grade II/VI at left sternal border (anemia-related)
• Respiratory: Clear; mild tachypnea
• Abdomen: Soft, non-tender; no hepatosplenomegaly
• Neurological: Decreased vibratory sensation bilateral ankles and toes (128 Hz tuning fork); decreased proprioception bilateral great toes; positive Romberg sign; bilateral Babinski signs (extensor plantar responses); diminished ankle reflexes; gait slightly wide-based
• Extremities: No edema; pallor of nail beds
• Psychiatric: Affect mildly flat; MMSE 27/30 (lost points on recall and attention)

Workup and Results

Laboratory Studies:

Imaging/Additional Studies:

• Peripheral blood smear: Macroovalocytes, hypersegmented neutrophils (> 5 lobes), anisocytosis, poikilocytosis
• MRI Brain and Spine: T2 hyperintensity in posterior columns of cervical and thoracic spinal cord (subacute combined degeneration); no intracranial abnormalities
• Nerve conduction studies: Axonal sensorimotor polyneuropathy predominantly affecting lower extremities

Clinical Image

Cross-sectional diagram of the spinal cord demonstrating subacute combined degeneration from vitamin B12 deficiency, showing demyelination of the posterior columns (proprioception, vibration) and lateral corticospinal tracts (upper motor neuron signs), with corresponding clinical manifestations. Source: Educational illustration.

Diagnosis

Severe Vitamin B12 Deficiency with Megaloblastic Anemia and Subacute Combined Degeneration of the Spinal Cord (ICD-10: D51.0, E53.8, G32.0)

Key Diagnostic Criteria:

• Serum B12 critically low (68 pg/mL; < 200 diagnostic)
• Markedly elevated methylmalonic acid and homocysteine (functional B12 deficiency biomarkers)
• Macrocytic anemia (MCV 118) with pancytopenia and classic smear findings (hypersegmented neutrophils)
• MRI evidence of subacute combined degeneration (posterior column T2 signal)
• Neurological examination consistent with dorsal column dysfunction (vibration, proprioception loss, Romberg positive) and corticospinal tract involvement (Babinski signs)
• Etiology: dietary deficiency (strict vegan without supplementation)

Treatment Plan

1. Urgent B12 Replacement: Intramuscular cyanocobalamin 1000 mcg daily for 7 days, then weekly for 4 weeks, then monthly indefinitely; IM route preferred over oral given neurological involvement and severity
2. Potassium Monitoring: Check potassium at 48 hours — rapid reticulocytosis can cause hypokalemia as potassium shifts into newly forming red cells
3. Reticulocyte Crisis Monitoring: Expect reticulocyte count peak at days 5-7 (confirms diagnosis and response to treatment)
4. Neurological Recovery Monitoring: Peripheral neuropathy may improve over months; posterior column lesions on MRI may partially or fully resolve; early treatment initiation is critical — neurological damage present > 6 months may be irreversible
5. Folate Supplementation: Add folic acid 1 mg daily (folate can mask hematological signs of B12 deficiency but will NOT prevent neurological damage — always replace B12 first)
6. Dietary Counseling: Vegan diet can be nutritionally complete with proper supplementation; lifelong B12 supplementation mandatory (minimum 250 mcg/day oral or 2500 mcg/week); recommend B12-fortified nutritional yeast, plant milks, and cereals as dietary sources; dietitian referral for comprehensive vegan nutrition planning
7. Screen for Other Deficiencies: Check vitamin D, omega-3 index, zinc, iodine — nutrients commonly insufficient in unsupplemented vegan diets
8. Family History Note: Mother's pernicious anemia is autoimmune and distinct from dietary deficiency, but patient should be monitored for future development of autoimmune gastritis (intrinsic factor and parietal cell antibodies currently negative)
9. Follow-up: CBC at 1 week (reticulocyte response), 1 month (Hgb improvement), 3 months (normalization); B12 and MMA at 3 months; repeat MRI spine at 6 months; neurological exam at each visit

Key Learning Points

• Vitamin B12 is exclusively produced by microorganisms and is found naturally only in animal-derived foods; strict vegans absolutely require supplementation or fortified foods — hepatic B12 stores can sustain a person for 3-5 years before deficiency manifests
• Methylmalonic acid (MMA) is the most specific biomarker for B12 deficiency and is elevated even when serum B12 is in the low-normal range; homocysteine is elevated in both B12 and folate deficiency and thus is less specific
• Subacute combined degeneration is a neurological emergency — the degree of neurological recovery is directly related to the duration of symptoms before treatment; neurological damage that has been present > 12 months is often irreversible
• Folate supplementation alone in a B12-deficient patient can correct the anemia (normalizing MCV and blood counts) while allowing neurological damage to progress silently — this is why it is critical to always check B12 before attributing macrocytic anemia to folate deficiency
• The peripheral blood smear finding of hypersegmented neutrophils (≥ 5 lobes in ≥ 5% of neutrophils, or any neutrophil with ≥ 6 lobes) is highly specific for megaloblastic anemia and should trigger immediate B12 and folate measurement

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