Pulmonary histiocytosis

　　The etiology of pulmonary histiocytosis is unknown. It is speculated that it may be related to immune function. Many scholars believe it is related to smoking, proposing the Bombesin theory, that the Bombesin-like neuropeptide substance produced by pulmonary neuroendocrine cells plays a leading role in the pathogenesis. And this substance is significantly elevated in smokers. Bombesin-like neuropeptide substance is a monocyte chemoattractant, a mitogen for epithelial cells and fibroblasts, which can promote cytokine secretion. In PHX, it has been found that this peptide can promote the occurrence of pulmonary tissue inflammation and fibrosis, which supports the above theory. Recently, some studies have found that there is an abnormal expression of adhesion molecules in PHX, but its direct relationship with the pathogenesis of PHX needs to be further clarified.

　　Pulmonary histiocytosis can be complicated by spontaneous pneumothorax and respiratory failure, and pulmonary heart disease may occur in the late stage. When pneumothorax occurs, reactive eosinophilic pleuritis can appear, with visible mesothelial hyperplasia, chronic inflammation, and eosinophilic infiltration, which is non-specific.Patients with end-stage pulmonary histiocytosis are accompanied by pulmonary hypertension, mainly related to the involvement of pulmonary small arteries and small veins, with visible media thickening and intimal hyperplasia in the vascular wall. Pulmonary Langerhans cells may participate in the reconstruction of pulmonary vessels by producing cytokines and growth factors..

　　Pulmonary histiocytosis can occur at any age, usually occurs in infants and children, but pulmonary involvement is usually not the main clinical manifestation. On the contrary, pulmonary histiocytosis that only involves the lungs often occurs in the age group of 20 to 40 years, with no significant gender difference. The clinical manifestations of pulmonary histiocytosis vary greatly. About 25% of patients have no clinical symptoms and are discovered incidentally during physical examination. Some patients are found to have X-ray findings when they have pneumothorax or respiratory symptoms.

　　The most common symptoms of patients are dry cough and dyspnea, other clinical symptoms include chest pain, fatigue, weight loss, and fever. About half of the patients have a history of rhinitis before onset. Hemoptysis is rare, less than 5%. About 25% of patients may have recurrent pneumothorax, and 4% to 20% of patients may have cystic bone lesions. Patients usually have focal bone pain or pathological fractures. A few patients may have central nervous system involvement, indicating poor prognosis. Auscultation usually does not show any abnormalities. 'Crackling sound' and 'claw-like fingers' are generally uncommon. Secondary pulmonary hypertension can be seen, but it is often overlooked. Pulmonary heart disease can occur in the late stage of the disease.

　　Pulmonary histiocytosis is a smoking-related interstitial lung disease. Quitting smoking can prevent its occurrence. At the same time, quitting smoking can also reduce the risk of lung cancer, chronic obstructive pulmonary disease, and cardiovascular and cerebrovascular diseases. Avoid exposure to harmful factors, avoid contact with harmful chemical substances, especially drugs, pay attention to rational drug use, and strengthen various protective measures when exposed to toxic or radioactive substances. Vigorously carry out health education activities for the prevention and treatment of various infectious diseases, especially viral infections. Strengthen physical exercise, pay attention to dietary hygiene, maintain a pleasant mood, combine work and rest, and enhance the body's resistance.

　　Routine laboratory tests for pulmonary histiocytosis usually do not show positive findings. The count of peripheral blood eosinophils is normal, routine blood biochemical tests usually show no abnormalities, and peripheral blood eosinophils are also usually normal. The erythrocyte sedimentation rate is generally moderately increased. Patients often have various low-titer autoantibodies and immune complexes, and the serum angiotensin-converting enzyme is normal.

　　1. X-ray manifestations:The chest X-ray manifestations vary with the different stages of the disease, and the lesions are usually bilateral and symmetrical. Although the lesions are diffuse, they are mainly concentrated in the middle and upper lung fields. In the early stage of the disease, the characteristic change is the indistinct shadow of small nodules (diameter less than 5mm), the most common change is reticular nodular shadow, and sometimes cystic lesions coexist. In the late stage, the nodular shadows usually disappear, and are replaced by pulmonary cystic changes and even pseudopneumonia formation. Some other manifestations can be distinguished from other diffuse lung diseases, including increased lung volume, lesions located in the upper lung, no mediastinal lymph node enlargement, and pleural involvement. Some patients may experience recurrent pneumothorax and osteolytic changes in the ribs. However, it should be noted that less than 19% of patients may have completely normal chest X-ray findings.

　　2. Chest CT examination:High-resolution CT (HRCT) is not only significant for the differential diagnosis of the disease but also has certain significance for judging the severity of the disease. The lesions are usually distributed in the normal lung tissue, although scattered lesions can be seen in the lower lung base. However, the lesions are mostly located in the upper part, showing a symmetrical and uniform distribution. Early lesions are mainly represented by indistinct small nodule shadows, and some cases may show the formation of cavities. The nodules are centrally distributed in the lobules and are accompanied by cystic changes with varying wall thickness. As the lesions progress, the cystic changes gradually become the prominent manifestation. These cystic cavities vary greatly in size, but are usually less than 1 cm in diameter. The cystic cavities can be solitary or merge with each other, even forming the manifestation of emphysema. The spontaneous appearance of small nodules, cavities, and cysticization are relatively characteristic changes of pulmonary Langerhans histiocytosis.

　　3. Pulmonary function examination:The pulmonary function changes in pulmonary Langerhans histiocytosis are related to the extent of lung involvement by the lung lesions, which can be obstructive, restrictive, or mixed ventilatory dysfunction. 10% to 15% of patients have normal pulmonary function, although chest X-ray findings have already shown abnormalities. The more common changes are a decrease in vital capacity (VC) and an increase in residual volume (RV), so the total lung capacity is normal, while the RV/TLC ratio is increased. This pulmonary function change is related to the patient's lung cysticization, and about 50% of patients have obstructive ventilatory dysfunction, manifested by a decrease in FEV1. If a patient with a diffuse pulmonary interstitial lesion has obstructive ventilatory dysfunction, it is a very useful indicator for diagnosing pulmonary Langerhans histiocytosis. The most common pulmonary function change is a decrease in diffusion function. The arterial oxygen partial pressure at rest can be normal or slightly decreased, but exercise-induced hypoxemia is most common.

　　4. Fiberoptic bronchoscopy and bronchoalveolar lavage examination:Under bronchoscopy, the bronchial mucosa can be seen to be normal or show non-specific inflammatory changes. Bronchial mucosal biopsy is not helpful for diagnosis, and transbronchial lung biopsy is usually not very meaningful for diagnosis due to the small size of the biopsy tissue. However, if the biopsy tissue is sufficiently large and the Langerhans histiocytic cells can be detected using immunohistochemical techniques, it is of great significance for diagnosis. The total cell count in most patients' bronchoalveolar lavage fluid (BALF) is increased, with a predominance of neutrophils and eosinophils. The CD4/CD8 ratio is decreased, and if the Langerhans histiocytic cells are greater than 5%, it strongly suggests the possibility of pulmonary Langerhans histiocytosis.

　　The diet of patients with pulmonary tissue cell hyperplasia should be light, easy to digest, with a lot of fruits and vegetables, a reasonable diet, and attention to adequate nutrition. In addition, patients should also pay attention to avoiding spicy, greasy, and cold foods.

　　Since pulmonary tissue cell hyperplasia is a rare disease and some patients can relieve it spontaneously, it is difficult to evaluate an effective treatment method. So far, there is no double-blind controlled trial to prove which treatment is effective. Oral corticosteroids are effective in controlling the symptoms of patients. The conventional dose is prednisone (prednisone). A recent study shows that corticosteroids can improve the symptoms and chest X-ray findings in patients who have just onset, but have no significant effect on pulmonary function improvement. Other cytotoxic drugs such as vincristine sulfate (vincristine) and etoposide (teniposide) are often used to treat diffuse tissue cell hyperplasia in children, but should be avoided in adult patients with only pulmonary involvement. Due to the close correlation between smoking and pulmonary tissue cell hyperplasia, every effort should be made to persuade patients to quit smoking.

　　Although it has not been proven so far that quitting smoking can improve the condition, quitting smoking can reduce the incidence of bronchogenic lung cancer, coronary heart disease, chronic obstructive pulmonary disease, and respiratory tract infections. Bronchitis and respiratory tract infections are the most common causes of acute exacerbation in patients with pulmonary tissue cell hyperplasia. The treatment of pneumothorax is the same as other methods, such as chest tube drainage or pleurodesis, but pleurodesis should be avoided as much as possible in patients who are about to undergo lung transplantation. For patients with advanced pulmonary tissue cell hyperplasia and severe pulmonary hypertension, lung transplantation treatment can be considered, but some patients may develop pulmonary tissue cell hyperplasia again after lung transplantation, accompanied by severe deterioration in pulmonary function. The impact of this complication on survival rate is not yet certain.