What is pernicious anemia?

What is Pernicious Anemia?

Pernicious anemia is an autoimmune disease characterized by antibody-induced destruction of gastric parietal cells, leading to intrinsic factor deficiency, impaired vitamin B12 absorption, and resulting megaloblastic anemia. 1

Pathophysiology

Pernicious anemia represents a late-stage manifestation of autoimmune gastritis where autoantibodies target:

• Parietal cells in the gastric corpus (producing gastric atrophy)
• Intrinsic factor (the protein essential for vitamin B12 intestinal absorption)

This autoimmune destruction prevents vitamin B12 binding and absorption in the gut, ultimately causing cobalamin deficiency 2, 3.

Clinical Presentation

The disease manifests with a triad of hematologic, neurologic, and gastrointestinal symptoms:

Hematologic Features

• Macrocytic anemia (elevated mean corpuscular volume)
• Fatigue and pallor (present in 55% of cases) 4
• Progressive weakness

Neurologic Manifestations

• Peripheral neuropathy with loss of sensation in limbs (32% of cases) 4
• Ataxia and gait disturbances
• Cognitive impairment and psychosis 2
• Critical point: Neurologic symptoms may present before anemia develops and can become irreversible if treatment is delayed 5, 6

Other Features

• Glossitis (sore tongue in 23% of cases) 4
• Weight loss (27% of cases) 4
• Gastric achlorhydria and atrophic gastritis 2

Diagnostic Approach

When pernicious anemia is suspected, obtain:

1. Complete blood count showing macrocytic anemia
2. Serum vitamin B12 level (typically low, but can be low-normal)
3. Methylmalonic acid (MMA) - elevated in B12 deficiency, confirms diagnosis even with low-normal B12 2
4. Anti-intrinsic factor antibodies - highly specific for pernicious anemia 3, 7
5. Anti-parietal cell antibodies - supportive but less specific 3

Endoscopy with topographical biopsies from corpus and antrum should be performed in newly diagnosed patients to:

• Confirm corpus-predominant atrophic gastritis
• Rule out gastric neoplasia and type 1 neuroendocrine tumors 3

Associated Conditions

Pernicious anemia frequently coexists with other autoimmune diseases:

• Autoimmune thyroid disease (up to one-third of patients) 3
• Type 1 diabetes mellitus 1
• Vitiligo 6

Screen all patients with pernicious anemia for thyroid disease 3.

Treatment Requirements

Pernicious anemia requires parenteral (intramuscular, subcutaneous, or intranasal) vitamin B12 treatment - oral supplementation is insufficient due to the intrinsic factor deficiency 2. This is a lifelong therapy requirement 8.

Long-term Complications

Patients face increased risk of:

• Gastric adenocarcinoma (2-4 fold increased risk) 3
• Type 1 gastric neuroendocrine tumors (0.4-0.7% annual incidence) 3
• Iron deficiency (due to achlorhydria) 3
• Irreversible neurologic damage if untreated 5, 9

Surveillance endoscopy should be performed to monitor for gastric neoplasia, though optimal intervals remain debated 3.

Key Clinical Pitfalls

• Do not wait for anemia to develop - neurologic symptoms may precede hematologic changes and become permanent 5
• Do not rely solely on serum B12 - use MMA to confirm deficiency in patients with low-normal B12 levels 2
• Do not prescribe oral B12 alone - parenteral replacement is mandatory in pernicious anemia 2
• Screen for iron deficiency concurrently - achlorhydria impairs iron absorption 3