Pernisiöanemia

Pernisiöanemia is a megaloblastic anemia most often caused by autoimmune destruction of the gastric parietal cells, which leads to a deficiency of intrinsic factor and impaired absorption of vitamin B12. Without intrinsic factor, dietary B12 is not effectively absorbed in the terminal ileum, resulting in vitamin B12 deficiency that affects blood cell formation and nerve function.

Pathophysiology involves autoantibodies against intrinsic factor or parietal cells, causing reduced intrinsic factor production. The resulting B12 deficiency impairs DNA synthesis in rapidly dividing cells, producing macrocytic red blood cells. B12 is also essential for myelin maintenance, so deficiency can cause neurological symptoms such as paresthesias, gait disturbances, and, in some cases, subacute combined degeneration of the spinal cord.

Clinical features commonly include fatigue, pallor, shortness of breath, and glossitis. Neurologic signs may appear early or later and can range from numbness and tingling to balance problems. Diagnostic workup shows macrocytic anemia with low reticulocyte count, low serum cobalamin levels, and elevated methylmalonic acid and homocysteine. Serologic testing may detect anti-intrinsic factor antibodies or anti-parietal cell antibodies. Endoscopy with biopsy can reveal autoimmune atrophic gastritis; the Schilling test is rarely used today.

Treatment consists of lifelong vitamin B12 replacement, typically via parenteral cyanocobalamin or hydroxocobalamin; high-dose oral B12 can be effective due to passive absorption. Hematologic response (reticulocytosis) usually occurs within days to weeks, and anemia within weeks, though neurologic recovery may be incomplete if treatment is delayed. Addressing concomitant autoimmune gastritis is recommended, with regular monitoring of B12 status.

Pernisiöanemia is more common in older adults and in individuals of Northern European descent, with increased risk linked to other autoimmune diseases. It is associated with a higher risk of autoimmune atrophic gastritis and, over time, gastric cancer and carcinoid tumors. With appropriate treatment, prognosis is generally favorable, though long-standing neurologic damage may be irreversible.