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Pernicious anemia (also known as vitamin B12 deficiency anemia, Biermer's anemia, Addison's anemia, or Addison–Biermer anemia) is one of many types of the larger family of megaloblastic anemias. One way pernicious anemia can develop is by loss of gastric parietal cells, which are responsible, in part, for the secretion of intrinsic factor, a protein essential for subsequent absorption of vitamin B12 in the ileum. The loss of ability to absorb vitamin B12 is the most common cause of adult B12 deficiency. A common underlying cause is atrophic gastritis with autoimmune destruction of gastric parietal cells (and autoantibody inactivation of intrinsic factor) leading to a lack of intrinsic factor. Absorption in the gut of vitamin B12 is normally dependent on intrinsic factor, which loss leads to vitamin B12 deficiency. The term ''pernicious anemia'' is sometimes also incorrectly used to indicate megaloblastic anemia due to any cause of B12 deficiency, its proper usage refers to that caused by atrophic gastritis, parietal cell loss, and lack of intrinsic factor only. Historically, pernicious anemia (PA) was detected only after causing symptoms and with well established anemia, i.e., liver stores of B12 had been depleted. The "pernicious" aspect of the disease – prior to the discovery of treatment – was a fatal prognosis. Modern tests which specifically target B12 absorption can diagnose the disease before it gives symptoms. Replacement of vitamin stores does not correct the defect in absorption from loss of intrinsic factor. Since the defect defines the disease, people without the ability to absorb B12 in this way will have pernicious anemia for the remainder of their lives. However, unless the patient has sustained permanent peripheral nerve damage before treatment, regular B12 replacement will keep PA in check, with no anemia and no further symptoms. Although initial treatment of the disease usually involves injections of B12 to rapidly replace body stores, a number of studies have shown long-term vitamin replacement treatment may be maintained with high-dose oral B12 supplements, since sufficient B12 is absorbed from these by a normal intestine, even without any intrinsic factor. In this regard, nasal and sublingual forms of B12 have not been found to have any special value over simple swallowed tablets.〔(【引用サイトリンク】url=http://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/ )〕 ==Signs and symptoms== Pernicious anemia presents insidiously, meaning that it slowly and subtly causes harm. Many of the signs and symptoms are due to anemia itself, where anemia is present. Untreated pernicious anemia can lead to neurological complications, and in serious cases, death. However, in 20% of cases of cobalamin deficiency, anemia is not observed.〔(【引用サイトリンク】title=Ferri: Ferri's Clinical Advisor 2012, 1st ed. )〕 While it may consist of the triad of paresthesias, sore tongue, and weakness, this is not the chief symptom complex. Common symptoms include anemia, fatigue,〔 depression, low-grade fevers, diarrhea,〔 dyspepsia,〔 weight loss,〔 neuropathic pain, jaundice, glossitis (swollen, red and smooth appearance of the tongue),〔 angular cheilitis (sores at the corner of the mouth),〔 dehydrated/cracked and pale lips and dark circles around the eyes (look of exhaustion),〔 brittle nails,〔 and thinning and early greying of the hair.〔 Because PA may affect the nervous system, symptoms may also include difficulty in proprioception, memory changes,〔 mild cognitive impairment (including difficulty concentrating and sluggish responses, colloquially referred to as brain fog), psychosis, impaired urination,〔 loss of sensation in the feet, unsteady gait,〔 difficulty in walking, muscle weakness〔 and clumsiness.〔 Anemia may cause tachycardia (rapid heartbeat)〔 and cardiac murmurs, along with a yellow waxy pallor,〔 low blood pressure, high blood pressure, and shortness of breath〔 (known as 'the sighs'). The deficiency also may present with thyroid disorders.〔 In severe cases, the anemia may cause evidence of congestive heart failure.〔 A complication of severe chronic PA is subacute combined degeneration of spinal cord, which leads to distal sensory loss (posterior column), absent ankle reflex, increased knee reflex response, and extensor plantar response. Other than anemia, hematological symptoms may include cytopenias, intramedullary hemolysis and pseudothrombotic microangiopathy. Pernicious anemia can contribute to a delay in physical growth in children, and may also be a cause for delay in puberty for adolescents. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pernicious anemia」の詳細全文を読む スポンサード リンク
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