Overview.
Pulmonary podoconiosis is the pulmonary manifestation of a fungal disease caused by infection with Histoplasma capsulatum. The lungs are the primary infection, mostly asymptomatic or self-limiting respiratory infections, and in severe cases may cause systemic dissemination.
Etiology
Histoplasma capsulatum is a biphasic fungus, mycelium type in the natural environment, with large and small spores, in the host tissue and nutrient-rich medium on the yeast-type organisms peripheral with a transparent band rather like a pod.
Histoplasma capsulatum spores inhaled through the respiratory tract, most of the body’s defense mechanism to eliminate, to reach the alveoli of the spores proliferation and transformation of yeast type. The spores proliferate and transform into yeast, causing neutrophils and macrophages to gather, and the yeast is phagocytosed by macrophages but not killed, and can still reproduce and reach the blood circulation through the hilar lymph nodes.
Symptoms
Incubation period 9 to 14 days.
1. Acute type
Most normal people do not show symptoms after infection. A few (mostly children) show upper respiratory tract infection or flu-like symptoms such as fever, cough and headache. Some may develop arthralgia-erythema nodosum-erythema multiforme syndrome, which lasts about 1 week. Pulmonary signs are minimal. After a large number of inhalation of spores, there may be chills, high fever, cough, cough mucopurulent sputum, dyspnea, hemoptysis and other symptoms of pneumonia, the duration of this type of disease is about 1 week, most of them can be self-healing, and a small number of them continue to progress.
2. Chronic cavity type
It mainly occurs in patients with emphysema, tuberculosis or destructive lesions of lung structure, because the abnormal cavities are conducive to the pathogenic bacteria to escape the interference of the body’s immune mechanism, and better reproduction. Clinical manifestations are very similar to those of tuberculosis, including low-grade fever, night sweats, weight loss, coughing, coughing up mucopurulent sputum, and gradual onset of respiratory distress. In addition to a small number of patients with self-cure, most of the progress, eventually leading to pulmonary fibrosis, often die of respiratory failure.
3. Progressive disseminated type
This type is rare and occurs in immunosuppressed patients or the elderly or children. Patients with severe systemic symptoms, often with high fever, dyspnea, hepatosplenomegaly, enlarged lymph nodes, jaundice, anemia, oral and gastrointestinal ulcers, endocarditis, meningitis and Addison’s disease. It progresses more rapidly in young children or AIDS patients, and relatively slowly in other patients, with a mortality rate of 80%.
Examination
1. Pathologic examination
Sputum, fiberscope brushing, lavage fluid fungal culture for more than 4 weeks, mycelial phase to yeast phase, visible its characteristic gear-shaped spores.
Pathological examination aims to find pathogenic bacteria, available silver staining, PAS staining and other special staining, if found in macrophages or leukocytes seem to have pods of yeast has a diagnostic value. Immunohistochemistry can be used to accurately identify the strain. Bone marrow, lymph node, secretion and biopsy culture are often positive in disseminated cases.
2. Histoplasmin skin test
The significance and method are similar to PPD (tuberculin pure protein derivative) skin test, and the results are observed 48～72 hours after the skin test, and ≥5mm red, swollen and hard nodules are regarded as positive. Positive skin test reveals that the patient has been or is being infected by Histoplasma capsulatum, and it has certain diagnostic value for patients in non-endemic areas. Generally, the skin test is positive 2-3 weeks after infection, and it can be maintained for several years. A negative skin test does not exclude the diagnosis.
3. Serologic test
Existing serologic antibody test has low specificity, and immunosuppressed patients can be false positive, which only suggests the diagnosis.
Complement binding test (CFT) is the main basis for clinical diagnosis, and it is generally believed that a potency ≥1:16 or a recent increase of more than 4 times is highly suggestive of active lesions. Immunodiffusion test (ID), specificity is higher than CFT, the appearance of “H” or “M” precipitation band is positive, the former often suggests active infection.
Enzyme-linked immunosorbent assay (ELISA) with a potency ≥ 1:16 is positive. In recent years, the histoplasmosis glycogen antigen (HAP) test has been carried out, and a positive test reveals active infection, which can provide a basis for early diagnosis. It has more diagnostic value for patients with immunodeficiency.
Diagnosis
According to the epidemiological data, clinical manifestations, X-ray signs and serological examination can be diagnosed, and the confirmation of diagnosis depends on fungal culture or histological examination to confirm the presence of pathogenic bacteria.
Differential diagnosis
This disease should be differentiated from tuberculosis, tuberculosis, bacterial pneumonia, viral pneumonia and lung cancer.
Treatment
Acute type usually does not need treatment, if the lesion is extensive and the symptoms are obvious, ketoconazole or fluconazole should be taken orally for 1~2 months. Chronic type and disseminated type need treatment. The chronic type is first treated with amphotericin B for 1 to 2 months and ketoconazole, maintenance therapy for 6 to 12 months. The disseminated type is preferred to be treated with amphotericin B, with ketoconazole or fluconazole after improvement. Fluconazole can also be given intravenously for at least 6 to 8 weeks, and ketoconazole treatment is not effective in patients with AIDS.