Eosinophilia is a disease process characterized by a persistently elevated blood eosinophil count (more than 1500 eosinophils/cubic millimeter), (a) Parasitic infections are the most common cause of eosinophilia. Unicellular protozoan infections generally do not cause eosinophilia, whereas multicellular helminth and trematode infections can cause eosinophilia, with the degree of increase paralleling the number and extent of worm, especially larval, infestation of tissues. Infections that are encapsulated within the tissues or confined to the intestinal lumen (roundworms, tapeworms) generally do not cause eosinophilia. However, parasites that can destroy the intestinal mucosa (hookworms) can cause eosinophilia. In clinical cases of unexplained eosinophilia, it is important to carefully understand the living environment and dietary history of the patient, and to examine the stool to detect eggs and larvae. However, some parasites such as Trichinella and filarial worms cannot be detected in the stool. Therefore, those with possible parasitic exposure, those with suspicion of colpus migrans such as asthma attacks, migratory pneumonia, and hepatomegaly must undergo relevant blood and histological tests to clarify the etiology. (B) Allergic diseases including allergic rhinitis, bronchial asthma, urticaria, angioneurotic edema and drug allergic reactions can present with eosinophilia. Allergic reactions to drugs can manifest only as eosinophilia, but can also cause interstitial nephritis, serum sickness, cholestatic xanthogranuloma, allergic vasculitis, and immunoblast lymphadenopathy. The drug should be discontinued as soon as drug fever and organ involvement occur. Drug-induced interstitial nephritis eosinophils are not only increased in the blood but also detected in the urine. (iii) Infectious diseases Certain acute bacterial and viral infections can cause an increase in eosinophils, which mostly return to normal during the recovery period, except for scarlet fever where eosinophils are still often increased during the recovery period. Some fungal (Aspergillus, Coccidioides) infections and individual chronic mycobacterial diseases can have eosinophilia. (D) Idiopathic hypereosinophilic syndrome is a myeloproliferative disease characterized by persistent and excessive eosinophil production. The diagnostic criteria are: ① absolute blood eosinophil count >1.
5 x 109/L (1500/mm3
) for more than six months; (ii) lack of a clear cause of eosinophilia; and (iii) signs and symptoms of organ involvement. The most serious and common complications are cardiac lesions with subendomyocardial thrombosis and fibrosis, leg cord fibrosis leading to atrioventricular regurgitation and eventually progressive congestive heart failure, which can be diagnosed and monitored by echocardiography. The nervous system is involved by emboli from the heart, diffuse encephalopathy and peripheral neuritis (polyneuritis mononeuritis). The skin, liver, spleen, respiratory and digestive systems are also frequently involved. The signs and symptoms of idiopathic hypereosinophilic syndrome are diverse, as the degree of damage varies with the organ it invades. Common ones include fever, cough, chest pain, palpitations, shortness of breath, neuropsychiatric symptoms, itchy skin rash, skin rash, angioneurotic edema, enlarged liver, spleen and lymph nodes, and heart murmurs. The prognosis is also poor in patients with severe involvement of major organs. However, there are patients without significant organ damage who have a benign course. Patients with angioneurotic edema and elevated IgE in this syndrome have a good prognosis, and the heart is rarely involved even in recurrent episodes. (E) Tumor eosinophilic leukemia is rare. In addition to fever, anemia, enlargement of the liver, spleen and lymph nodes, which are common in leukemia, symptoms of cardiac, pulmonary, neurological and skin infiltration are more prominent in this disease. Chronic granulocytic leukemia is seen as eosinophilia, often with basophilia. Some subtypes of acute non-lymphoblastic leukemia may have eosinophilia. Eosinophilia is seen in the blood, bone marrow, and lymph nodes of patients with Hodgkin’s disease. Eosinophilia may also be seen in the blood of a few carcinomas, especially those of mucin-producing epithelial origin, those that metastasize to the plasma membrane and bone, and those with necrosis at the center of the lesion and sarcomas. Eosinophilic granulomas mainly invade bone tissue. (F) A variety of skin diseases, including the above-mentioned tumors, scabies, scabies, scarring dermatitis, exfoliative dermatitis, eczema, scarring in pregnancy and itchy zonular papules and plaque syndrome, psoriasis, and episodic angioneurotic edema, can be associated with eosinophilia. (vii) Pulmonary infiltra-tion with eosinophilia (PIE) is a not uncommon group of eosinophilic infiltrates,
PIE is a group of not uncommon diseases. The pathogenesis is mostly related to an abnormal immune response, but the etiology is uncertain. (viii) Gastrointestinal diseases with eosinophilic gastroenteritis are associated with allergic reactions and manifest as dyspepsia, abdominal pain, diarrhea and fever. The peripheral blood leukocyte classification can be as high as 60% or more eosinophils, and there can be extensive infiltration of eosinophils from the mucosa to the plasma membrane layer of the gastrointestinal tract. The disease can last for more than 10 years and is often self-limiting. Increased eosinophils are present at the foci of ulcerative colitis. Eosinophilia can sometimes be present in the blood of patients with ulcerative colitis and clonorchiasis. (ix) Immune diseases rheumatic diseases (SLE, rheumatoid arthritis, polyarteritis nodosa, dermatomyositis, etc.), allergic vasculitis and granulomatous vasculitis, some congenital immunodeficiencies, eosinophilic fasciitis after drug treatment and graft-versus-host reactions, etc. often have eosinophilia. (J) Other plasma membrane surface irritation, such as inflammation, abdominal irradiation, long-term peritoneal dialysis, injury or repeated punctures, can cause plasma membrane cavity effusion and eosinophilia in the blood. Severe toxic diseases, eosinophilic myalgia syndrome, adrenal and pituitary hypofunction can cause eosinophilia. Diagnosis
Eosinophilia is diagnosed by an increase in the absolute value of eosinophils in the peripheral blood. The key is the etiological diagnosis, which requires a thorough medical history and a comprehensive physical examination, as well as the use of necessary auxiliary diagnostic methods to identify the primary lesion. Those who are not sure of the cause should be followed up regularly.