What is Pernicious Anaemia ?

Pernicious anaemia (PA) is an autoimmune disease in which the body’s immune system attacks the stomach lining, specifically the parietal cells that produce intrinsic factor—a protein essential for absorbing vitamin B12 from food. Without functioning intrinsic factor, B12 cannot be absorbed effectively in the ileum, leading to deficiency. This deficiency impairs DNA synthesis, red blood cell production, and neurological function. If untreated, it can cause severe anaemia and irreversible nerve damage.

Understanding the Biochemistry

In a healthy person:

  • Parietal cells in the stomach lining produce intrinsic factor (IF) and hydrochloric acid.
  • IF binds to dietary B12, enabling its absorption.
  • Vitamin B12, together with folate, is critical for producing healthy red blood cells (RBCs) in the bone marrow.
  • RBCs carry oxygen via haemoglobin (which requires iron).

In PA, autoimmune attack destroys parietal cells and/or neutralises intrinsic factor via antibodies. This results in B12 malabsorption, deficiency, and megaloblastic (abnormally large and dysfunctional) RBCs in many cases. Not all patients develop classic macrocytosis, however.

Think of a maturing RBC as a bus being built. B12 (and folate) provides essential raw materials for proper assembly. Without them, the “bus” is malformed and cannot effectively load or transport oxygen molecules (via haemoglobin) to tissues. The result is anaemia (“lack of healthy blood”) and widespread oxygen deprivation.

red blood cells

Importance of Neurological Symptoms

Neurological symptoms are a critical and sometimes early feature of B12 deficiency in PA. They can include pins and needles (paraesthesia), numbness, balance problems, gait disturbances, cognitive difficulties (“brain fog”), memory issues, mood changes, or even more severe problems like subacute combined degeneration of the spinal cord. Importantly, these symptoms can occur with or without anaemia and/or macrocytosis. Relying solely on blood count abnormalities may delay diagnosis and allow irreversible nerve damage. Prompt treatment is essential to prevent long-term neurological consequences.

Autoimmune Aspects and Co-existing Conditions

PA is one of many autoimmune diseases (e.g., alongside Type 1 diabetes, Hashimoto’s thyroiditis, vitiligo, or multiple sclerosis). Patients with one autoimmune condition are at increased risk of developing others. Hashimoto’s thyroiditis is particularly common in those with PA.
Diagnostic Antibodies:
Intrinsic Factor Antibodies (IF Ab): Highly specific for PA. A positive result strongly supports the diagnosis and the need for lifelong B12 replacement. Sensitivity is around 50–70% (varies by assay and disease stage), so a negative result does not exclude PA.
Parietal Cell Antibodies (PCA): More sensitive but less specific (present in some healthy individuals). Useful as supporting evidence but not diagnostic alone.

Diagnosis integrates clinical symptoms, B12 levels (or active B12/MMA/homocysteine where appropriate), antibody results, and exclusion of other causes. Endoscopy with biopsy may be used for confirmation in some cases.

Symptoms and Presentation

Symptoms vary widely and can occur without anaemia or macrocytosis:

  • Fatigue, weakness, shortness of breath.
  • Neurological: pins and needles, numbness, balance problems, cognitive “brain fog,” memory issues.
  • Glossitis (sore, smooth tongue), gastrointestinal issues.
  • Other: mood changes, visual disturbances, etc.

Key point: Modern guidelines stress not ruling out B12 deficiency based solely on normal blood counts.

Historical Context and Treatment

Before effective treatment, PA was often fatal—hence “pernicious.” Breakthroughs (including Nobel Prize-winning work) led to liver therapy in the 1920s and injectable B12 after WWII. Today, with prompt diagnosis and lifelong B12 replacement (typically intramuscular hydroxocobalamin in cases of malabsorption), the life-threatening anaemia is preventable. However, some patients continue to experience persistent symptoms even after haematological correction, highlighting the need for ongoing research and individualised management.
British Committee for Standards in Haematology (BCSH) guidance notes that a positive IF antibody test identifies patients needing lifelong cobalamin replacement. Treatment should never be stopped arbitrarily.

Prevalence and Challenges

Estimates suggest B12 deficiency affects a significant portion of the population (often cited around 6–10% or higher depending on criteria), with PA being a major non-dietary cause, especially in older adults. Exact figures for PA are difficult due to inconsistent diagnostic thresholds, imperfect tests, and under-recognition. Many cases may be missed if relying solely on IF antibody testing or waiting for macrocytosis.

Summary

Pernicious anaemia is a lifelong autoimmune condition causing B12 malabsorption due to loss of intrinsic factor. It requires prompt diagnosis and lifelong replacement therapy (preferably bypassing the gut). While the anaemia itself can be corrected, the underlying autoimmunity persists, and some patients face ongoing challenges. Greater awareness, better testing strategies, and research into persistent symptoms are essential.

References

  1. NICE. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239). March 2024.
  2. Devalia V, Hamilton MS, Molloy AM. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br J Haematol. 2014;166(4):496-513.
  3. Hooper M. What You Need to Know About Pernicious Anaemia and Vitamin B12 Deficiency. Hammersmith Health Books; 2014 (or latest edition).

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