Pneumocystis carinii pneumonia

　　The Pneumocystis carinii is a unicellular organism that exhibits characteristics of both protozoa and fungi. Pneumocystis carinii mainly exists in two forms: cysts and trophozoites. Trophozoites are variable in shape, with fine pseudopodia and false feet, resembling amoebas. Cysts are circular, with a diameter of 4-6 μm, and the inner wall of the cyst contains intracystic bodies (also known as sporozoites). Generally, mature cysts contain 8 intracystic bodies. Cysts are an important diagnostic form. The寄生部位 of Pneumocystis carinii is limited to the alveolar cavity. After mature cysts enter the alveoli, they break open, and the intracystic bodies disencyst and develop into trophozoites. Trophozoites寄生于肺泡上皮，proliferate, and cysts are often located in the central part of the alveoli.

　　Pneumocystis is a low-pathogenic, slow-growing parasitic protozoan. Healthy hosts have resistance and only form asymptomatic infections. Impaired cell-mediated immunity is the main predisposing factor for the host, such as malnutrition in infants and children with congenital immune deficiency, malignant tumors, organ transplantation, or patients receiving immunosuppressive therapy and AIDS patients. The incidence in AIDS patients is as high as 80% to 90%. When T cell-mediated immunity is suppressed, the Pneumocystis in the alveoli can multiply in large numbers, causing direct toxic damage to the epithelial cells, leading to type I epithelial desquamative alveolitis. The alveolar septum has infiltration of plasma cells and monocytes, with hyperplasia and thickening of the alveolar epithelium, and the alveolar lumen is filled with eosinophilic foamy substances and proteinaceous exudates. In severe cases, there is widespread interstitial and alveolar edema. The alveolar lumen is filled with inflammatory cells, proteinaceous exudates, and parasites, hindering gas exchange and causing clinical symptoms.

　　Pneumocystis carinii is an acute pulmonary disease caused by the寄生 in human alveoli, also known as Pneumocystis carinii pneumonia or Pneumocystis carinii disease. It often occurs in AIDS patients and is the main cause of opportunistic infection-related mortality. Clinical symptoms are mainly characterized by fever, cough, and dyspnea, with rapid progression and a high mortality rate. Without treatment, almost 100% die of respiratory failure.

　　Pneumocystis carinii pneumonia is difficult to diagnose. Diagnosis can be considered in high-risk populations based on clinical manifestations and X-ray examination, and confirmed by further examination of the pathogen. The positive rate of finding the pathogen in sputum is extremely low, and sputum induction can be induced by atomizing 3% hypertonic saline. Bronchoalveolar lavage (BAL) and transbronchial lung biopsy have a positive rate of up to 80% to 100%. BAL can detect Pneumocystis at the same time as anatomical examination and is useful for early diagnosis. Thoracotomy biopsy has a high positive rate but is not easily accepted by patients, and is dangerous for those with severe illness, and is rarely used now. In recent years, thoracoscopy biopsy has been advocated to replace thoracotomy biopsy.

　　Epidemic infantile type (classic type) is prevalent in nurseries, with a slow onset, initially with anorexia, diarrhea, low fever, followed by cough and dyspnea, with progressive worsening of symptoms. The mortality rate without treatment is 20% to 50%.

　　Acute onset of pediatric-adult type (modern type) is rapid, with dry cough at the beginning, followed by high fever, dyspnea, cyanosis, and few lung signs. Hepatosplenomegaly may occur. The typical course from onset to diagnosis is 1-2 weeks, with short duration of illness and death within 4-8 days in those receiving high-dose hormone therapy. The course of AIDS patients is more gradual and progressive, with initial weight loss, night sweats, lymphadenopathy, and general malaise, followed by the above respiratory symptoms, which may last for several weeks to several months. Without treatment, 100% die of respiratory failure. The symptoms of this disease are severe, but there are few lung signs, with most patients having no abnormal findings on lung auscultation, and some patients may hear scattered moist rales.

　　Pneumocystis carinii pneumonia should pay attention to isolation of immunosuppressed individuals and patients to prevent cross-infection. High-risk populations should be closely monitored. For patients at risk of Pneumocystis carinii infection, drug prophylaxis can be used to effectively prevent the potential infection from becoming a clinical disease and the recurrence after treatment. Generally, TMP 5mg/kg, SMZ 25mg/kg, taken orally once or three times a day or a week. Nebulized pentamidine can be used as a second-line prophylactic medication.

　　The diagnosis of Pneumocystis carinii pneumonia can be confirmed based on the following examinations:

　　1. Hematological examination

　　White blood cell count is increased or normal, related to the underlying disease, with a slight increase in eosinophils and an increase in serum lactate dehydrogenase.

　　2. Blood gas and pulmonary function

　　Arterial blood gas often shows hypoxemia and respiratory alkalosis, with a decrease in lung vital capacity and a pulmonary diffusion function (DLCO) below 70% of the estimated value in pulmonary function tests.

　　3. Pathogen examination

　　Sputum, bronchoalveolar lavage fluid, and lung biopsy through bronchoscope can be used for specific staining such as Giemsa staining, methylene blue (TBO) staining, Gomori's methylene blue silver (GMS) staining, and the detection of cysts containing 8 intracystic bodies as the basis for diagnosis.

　　4. Serological examination

　　Currently common methods include the detection of antigens by convection immunoelectrophoresis, indirect fluorescence tests, immunoblotting tests, detection of antibodies and complement fixation tests in serum, but they lack good sensitivity and specificity and cannot be used for the diagnosis of Pneumocystis carinii pneumonia.

　　The X-ray manifestations are non-specific. Up to 10% to 25% of patients may have normal chest X-rays. The typical X-ray manifestation is diffuse interstitial lung infiltration, mainly in the form of reticular nodular shadows, extending outward from the hilum. As the condition progresses, it rapidly develops into pulmonary consolidation, with widespread lesions distributed in a centrifugal manner, similar to pulmonary edema. There may be emphysema and small areas of atelectasis among the consolidation foci, most prominent around the periphery of the lung. Chest wall lesions such as pneumothorax or pleural effusion are rare. There may also be limited nodular shadows and unilateral infiltration as manifestations, with a decrease in lung vital capacity and a pulmonary diffusion function (DLCO) below 70% of the estimated value in pulmonary function tests.

　　Patients with Pneumocystis carinii pneumonia should have a diversified diet, eat more high-protein, high-vitamin, low-animal-fat, easily digestible foods, and fresh fruits and vegetables. They should avoid eating stale, deteriorated, or刺激性 things, eat less smoked, roasted, pickled, fried, or overly salty foods, and balance their staple foods with coarse and fine grains to ensure nutritional balance.

　　Vegetables, melons, beans, and other foods are rich in various vitamins and trace elements, and have certain anticancer and antitumor effects. For example, soybeans, cabbage, and Chinese cabbage contain abundant trace element molybdenum, while tomatoes, carrots, amaranth, and jujube are rich in vitamin A, C, and B vitamins, among others.

　　Pneumocystis carinii pneumonia has a high mortality rate, but the early treatment response is good, and most patients can recover, so the key lies in early diagnosis and treatment.

　　1. General treatment Patients should rest in bed, increase nutrition, correct electrolyte and water and electrolyte imbalances. Correct hypoxia, oxygenate through the nose or face mask, and use assisted ventilation or extracorporeal membrane oxygenation for severe hypoxia when the arterial oxygen partial pressure is above 9.32kPa (70mmHg) when FiO2 is less than 50%. Try to reduce the use of immunosuppressants, but for patients with severe diffuse lesions, especially AIDS patients, short-term use of corticosteroids such as prednisolone 40mg, once every 6 hours, for 7 days, should be considered.

　　2. Etiological treatment

　　(1) Sulfamethoxazole/trimethoprim (SMX-TMP): It is currently an ideal treatment drug, with an initial treatment effective rate of 77%. The general dose of trimethoprim (TMP) is 20mg/kg per day, and sulfamethoxazole (SMZ) is 100mg/kg per day, administered intravenously or in four divided doses orally. For severe cases, intravenous injection is used, and oral administration can be changed after 7 to 10 days when the condition improves, with a minimum course of 14 days. Side effects include rash, increased transaminases, neutropenia, increased blood creatinine, etc., and more than half of AIDS patients may experience adverse reactions.

　　(2) Pentamidine: It has a lethal effect on pneumocystis, but the incidence of adverse reactions can reach 50%. The dose is 4mg/kg, intramuscular injection, once a day, for 14 days. The initial treatment effective rate is 70%, and the re-treatment effective rate is 50%. The缺点 is that there are serious adverse reactions, mainly renal, hypoglycemia, orthostatic hypotension, leukopenia and thrombocytopenia, nausea and vomiting, and pain and abscesses at the site of intramuscular injection. At present, it is recommended to use it when conventional drugs cannot be tolerated or are ineffective, and it can still achieve certain efficacy. There are reports that pentamidine inhalation therapy, 40mg/kg, once a day, has achieved satisfactory efficacy.

　　In recent years, it has been found that Pneumocystis carinii pneumonia (PCP) is the most common opportunistic infection in AIDS patients and the main cause of death for them.