Cryptococcosis is an acute, subacute or chronic fungal disease caused by Cryptococcus spp. that most often infects the brain, lung, bone or skin. In recent years, there has been a gradual increase in the incidence of cryptococcosis, which can infect both immunocompetent and immunocompromised hosts. Among them, cryptococcal meningitis is the most common, followed by lung and skin infections [1].
I. Epidemiology
The disease is distributed worldwide, and the annual incidence of pulmonary cryptococcosis in immunocompetent hosts is about 0.4/100,000 to 0.9/100,000, while the annual incidence in immunocompromised individuals, especially those with HIV infection, is about 6-10%. Data from the United States show that the most common pathogens in 140 patients with pulmonary fungal infections from 1988 to 1997 were Aspergillus (57%), Cryptococcus (21%) and Candida (14%) in that order. China has seen cases reported in Shanghai, Jiangsu, Zhejiang, Heilongjiang, Jilin, Guangdong, Guangxi, Hunan, Hubei, Yunnan, Chongqing and more than 10 provinces. The pathogenic spectrum of pulmonary fungal infections was investigated in Peking Union Medical College Hospital from 1986 to 1998, and the incidence of Cryptococcus pulmonarius infection ranked 5th after Candida (79.5%), Aspergillus (11.8%), Trichoderma (3.9%), and Penicillium (3.9%), at 0.78%. The incidence rate of pulmonary cryptococcal infection was 13.4% among patients with Aspergillus, Cryptococcus, Trichoderma, and Candida in that order; if only patients with confirmed and clinical diagnosis were counted, the incidence rate of pulmonary cryptococcal infection was 20.9%. Among the 75 cases of deep fungal infections confirmed by autopsy in the PLA General Hospital from 1955 to 1991, the incidence was Aspergillus (53.5%), Candida (33.3%), Cryptococcus neoformans (6.9%) and Trichoderma (5.8%) in order, and Cryptococcus mainly invaded the meninges and lungs. In recent years, the incidence of cryptococcosis has been increasing and has become one of the most common complications of AIDS in foreign countries, as well as the leading cause of death in AIDS patients. The annual incidence rate in immunocompetent people is reported to be 0.2%, while the annual incidence rate in AIDS patients is 80% to 90%. Pulmonary cryptococcosis is second only to pulmonary aspergillosis in the overall pulmonary fungal lesions, accounting for about 20%. Cryptococcosis can be primary in a few cases and secondary in most; there is no evidence of intra-hospital outbreaks of transmission; there is no animal-to-human transmission, and human-to-human transmission has been reported. Pulmonary cryptococcosis can occur at any age, children are rare, 40 to 60 years of age is common; susceptible to infection of men, the ratio of men to women in HIV-negative people is about 2:1, HIV-positive people is 5:1 to 11:1.
II. Pathogenesis
In 1894 Sanfelice first isolated a new fungus in peach juice and named it new yeast. Until 1950 Benham finally named it as Cryptococcus neoformans. The genus Cryptococcus, with 37 species and 9 varieties, is a saprophytic parasitic yeast that is widely distributed throughout the world and can be isolated from soil, pigeon droppings and fruits, as well as from the skin, mucous membranes and feces of healthy humans. Pigeon droppings are the natural host of Cryptococcus neoformans new variants and are considered the most important source of infection. The aerosol particles formed by flying dried pigeon droppings are often less than 2 μm in diameter and easily reach the alveoli. Cryptococcus neoformans is a round or ovoid yeast, 4 to 17 μm in diameter; in solid medium, most strains are mucilaginous, do not form hyphae and spores, rely on germination reproduction, generally single bud, thick wall. Most of the strains have wide and thick pods wrapped, the pods are composed of mucopolysaccharide, about 3-5μm thick. in HE stained tissue sections, cryptococci are light red, not easy to see. In HE stained sections, Cryptococcus is pale red and not easily visible, but it is clearly visible with PAS or silverophilic staining. There are three variants of Cryptococcus neoformans, namely var neoformans, var gattii and var grubii. The Gert variant is mainly distributed in tropical and subtropical regions, and the Shanghai variant is from non-immunosuppressed patients in Shanghai, but more than 90% of cryptococcosis is caused by Cryptococcus neoformans neoformans variant. According to its podococcal antigenicity, Cryptococcus is divided into 5 serotypes A, AD, D, B and C. In addition, there are a few indeterminate types. type A is widely distributed around the world, types B and C are mainly distributed in Central Africa and Southern California in the United States, and type D is more common in Europe [2]. Types A, B, D and AD exist in China, with type A being the most common, followed by types B and D. Type C has not been found. Podoconjugate antigens are soluble in cerebrospinal fluid, serum and urine, and can be detected by specific serum.
III. Pathogenesis
Cryptococcosis infection may have several pathways: inhalation of airborne cryptococcal spores through the respiratory tract is the main route of cryptococcal infection; it can also be caused by traumatic skin inoculation, or by eating food with bacteria entering the body through the digestive tract, or by becoming a carrier. Healthy people are not easily infected with Cryptococcus neoformans, only when the body resistance is reduced, the pathogenic bacteria are easy to invade the host body, causing cryptococcosis. Pigeon droppings are considered the most important source of infection, and animals that can isolate the bacterium include horses, cows, dogs, cats, mountain antelopes, mink, pigs, koalas, rats, etc. The first inhaled spores are deposited in the lungs and do not have pods; 24 hours after invading the host the spores acquire pods and thus acquire pathogenicity.
The lungs are the first site of infection. Cryptococci enter the lung and have 3 forms of manifestation: ① Cryptococcal colonization: can be colonized in the airways or alveoli, no symptoms, no imaging changes, common in patients with chronic lung disease; ② Cryptococcal aggregation: the organism grows in the alveoli but does not cause the inflammatory response of the body; ③ Granuloma formation: pathological changes are manifested as yellow-white or pink gelatinous translucent material visible to the naked eye in the early stage, and in the late stage as granulomas of varying sizes, with caseous necrosis and small cavities visible in the lesions, without calcification and no obvious surrounding envelope. Pulmonary cryptococcal infection in the absence of any primary pulmonary pathology and lung structural abnormalities is called primary cryptococcal pneumonia and occurs in approximately 50% of immunocompetent patients, with the majority of patients having a single affected organ in the lung [3].
The immune function status of the host determines the clinical and radiological manifestations associated with cryptococcal infections. Factors predisposing to cryptococcosis include chronic wasting diseases such as diabetes, nodular disease, leukemia, advanced tumors, AIDS, and organ transplant patients. Inhalation of cryptococci can cause intrapulmonary infection in normal individuals, but often only imaging abnormalities are present, with few symptoms and often a tendency to heal spontaneously. In patients with immune impairment, the fungus forms foci in the lungs after inhalation, and can spread systemically via bloodstream, and mostly invades the central nervous system. the anti-cryptococcal immunity of monocytes is reduced in HIV-infected patients, while cryptococcal antigens reduce cell-mediated immunity, making it easier for cryptococci to survive in the host [1].
IV. Pathological changes
Almost all cryptococcosis is caused by neoplastic cryptococci, which cause a chronic inflammatory response in the tissues. The lesions are related to the early stage of the disease, with early formation of gelatinous lesions with a mild inflammatory response, few neutrophils and only a few lymphocytes and histiocytes infiltrating. A large number of cryptococci are seen in freshly active lesions. Late lesions are granulomatous with fibrous tissue proliferation with a large number of macrophages, foreign body giant cells and lymphocytes, most of which can have cryptococci in their cytoplasm, and later lesions can be surrounded by fibrous tissue or form fibrous scars. The type of lesion is related to the patient’s immune status, with immunocompetent individuals often forming non-caseating granulomatous lesions containing phagocytosed cryptococci within the cytoplasm of macrophages; whereas immunocompromised individuals are less likely to see granuloma formation and will be filled with cryptococcal spores in the alveolar cavity, with inflammatory cells being rare; necrosis and cavitation are rare. There are three common pathological types of pulmonary cryptococcosis: isolated granulomatous type, cornified granulomatous type and pneumonia type. The latter two types are mainly seen in immunocompromised or chronically immunosuppressed patients and can involve multiple lobes of the lung; isolated granulomatous type is mostly seen in patients with normal immunity and can also show involvement of multiple lobes of the lung. Cryptococcosis of the central nervous system mainly manifests as meningitis. Later granulomatous lesions can occur in the meninges, brain parenchyma and spinal cord [1].
V. Clinical manifestations
1, Pulmonary cryptococcosis: a subacute or chronic visceral fungal disease caused by Cryptococcus neoformans infection. Pulmonary cryptococcosis can exist alone or occur in conjunction with cryptococcosis at other sites. About 1/3 to half of those with pulmonary lesions present with a nodular lung shadow without any symptoms, often detected on chest x-ray, and sometimes misdiagnosed as tuberculosis or lung cancer (asymptomatic type). Some patients have an insidious onset with a mild cough, a small amount of mucus sputum or blood sputum, chest pain, low fever, malaise and weight loss (chronic type). A few cases show acute pneumonia with high fever, shortness of breath, and hypoxemia, which may lead to acute respiratory failure; occasionally, there are signs of chest pain or solid lung changes and pleural effusion (acute type), which are mostly seen in AIDS patients. When complicated by encephalomyelitis, the symptoms are obvious and severe. There is often moderate fever, occasionally high fever reaching 40°C, and signs and symptoms of meningoencephalitis [1]. On examination, in addition to shortness of breath and cyanosis, fine wet rales can sometimes be heard in both lungs, and in rare patients, pleural effusion is present with corresponding clinical signs.
Radiographic manifestations of pulmonary cryptococcosis: most often bilateral multiple lesions, but also unilateral or confined to one lobe of the lung, and its manifestations can be of various types. (1) isolated mass shadow, about 2cm~7cm in diameter, mostly seen in primary pulmonary cryptococcosis; (2) single or multiple nodular shadow; (3) single or multiple patchy shadow, with cavity formation in about 10% of patients, often secondary to pulmonary cryptococcosis; (4) diffuse corn-like shadow; (5) acute interstitial pneumonia type, which is rare. Calcification and caseous necrosis are rare in all types, but calcification and cavity formation have also been reported. It has been suggested that in AIDS patients, interstitial lung changes and hilar lymph node enlargement are common, while in non-AIDS patients, mainly mass or solid shadows are seen, while pulmonary atelectasis, lymph node enlargement, pleural effusion and abscess chest are rare. The X-ray manifestation of pulmonary cryptococcosis has no specific changes and is easily confused with lung cancer, pulmonary metastatic tumors, pulmonary tuberculosis, and Wegener’s granulomatosis. Especially, isolated large spherical foci are not easily distinguished from lung cancer.
CT manifestation: CT is one of the important means to diagnose pulmonary cryptococcosis. With the widespread use of thin layer and high resolution CT, the CT performance of pulmonary cryptococcosis shows certain characteristics. The main manifestations are: ① Bronchial infiltrative solid lesions, mostly limited infiltrative solid lesions, lesions of different sizes and morphology, single or multiple infiltrative lesions. They may be small lamellar or mass-like lesions or single or multiple lobar lesions with blurred borders and uneven density, and may be seen as “bronchial gas” or “vacuolation”, with some necrotic cavities. The nodules vary in size from 0.5 to 6 cm in diameter, or even larger, with clear borders, irregular morphology, lobarization and burr. 40% of the lesions have hairy glass-like blurring around the periphery or adjacent lung field ring, called “halo sign”. Most of the lesions are located in the outer lung zone and subpleural area, and may have smooth cavity formation and involvement of the pleura. Individual lesions may have burr and “pleural depression sign”, which are not easily distinguished from lung cancer. ③ Diffuse mixed lesions, showing the coexistence of nodules, patches, masses, and lobar solid lesions. In conclusion, CT manifestations of pulmonary cryptococcosis are diverse and non-specific. The lesions are mostly seen in both lower lungs, with multiple nodular foci, masses, and lamellar exudative shadows in normally immunized adults, while exudative shadows are more common in immunocompromised adults and children, and confirming the diagnosis depends on pathological examination [4].
2, other sites of cryptococcosis: ① Cryptococcal meningitis: central nervous system infection with cryptococcal meningitis is the most common, accounting for more than 80% of cryptococcosis. According to retrospective analysis about 37% of HIV-negative cryptococcosis patients have cryptococcal meningitis, and about 6% to 11% of AIDS patients will contract cryptococcal meningitis. The mortality rate of this disease is high (20% to 30%). ② Skin and mucosal cryptococcosis: Rarely occurs alone, often coexists with meningeal and pulmonary lesions, often occurs in the nasal septum, gums, tongue, hard jaw, soft jaw, tonsils, throat, and skin of the face and neck, chest and back, and extremities, initially as molluscum contagiosum-like or acne-like papules, nodules or abscesses, followed by central ulceration and a small amount of pus with mucus blood, containing cryptococci. Bone and joint cryptococcosis: rarely occurs alone, the whole body can be involved in bones, but the bony prominence, skull and spine are more. The joints are rarely involved and are often secondary to adjacent skeletal lesions. The lesions progress slowly. Visceral cryptococcosis: It is caused by dissemination and often affects the heart, testes, prostate, and eyes, but not the kidneys, liver, spleen, or lymph nodes. Infections of the gastrointestinal tract and genitourinary system are similar to those of tuberculosis [1].
VI. Diagnosis
1. Pathogenic examination: it is an important basis for the diagnosis of pulmonary neoplastic cryptococcosis, and specimens should be collected for smear and culture as many times and in as many ways as possible for the proposed cases.
The positive rate of sputum culture and smear examination is generally less than 25%, and because Cryptococcus neoformans can reside in the normal population, sputum or even tracheal flush culture of Cryptococcus neoformans should be judged according to the clinical situation whether it is a pulmonary cryptococcal infection. When Cryptococcus neoformans is isolated from a patient with AIDS, a high degree of caution should be exercised.
In cases of suspected pulmonary cryptococcal infection, every effort should be made to perform invasive tests to collect tissue specimens for pathogenic testing when conditions permit. If the specimen is obtained from a percutaneous lung puncture biopsy or fine needle aspiration, or from a fiberoptic bronchoscopic anticontamination brush specimen, microscopic examination and/or culture of Cryptococcus neoformans is of diagnostic value.
It is worth noting that immunocompetent patients with pulmonary cryptococcal infection are more likely to have systemic dissemination, especially with central nervous system invasion, and extra-pulmonary dissemination is more likely if such patients are clearly diagnosed with or treated by surgical pathology. Therefore, cerebrospinal fluid examination should be performed as soon as possible for suspected meningitis, and the positive rate of cerebrospinal fluid smear for early meningitis can be more than 85%, and the positive rate of culture is also higher. There is no definitive answer to the need for routine cerebrospinal fluid examination in patients diagnosed with pulmonary cryptococcosis, but it is preferred that cerebrospinal fluid examination be performed in patients with immune abnormalities.
Immunological tests: The thick pods of cryptococci contain specific antigenic polysaccharides, and this antigen or corresponding antibodies can be detected in the serum or cerebrospinal fluid of about 90% of patients with cryptococcal meningitis. The clinical value of antibody detection is not high because there are not many detectable antibodies in the patient’s serum, and the specificity is not strong, and the false positive rate is high, so the clinical use is antigen detection, that is, the application of latex agglutination test to detect cryptococcal podococcal polysaccharide antigen, which is a simple, rapid, sensitive and specific detection method, and is the main means of early diagnosis. The positive rate of cerebrospinal fluid antigen in patients with meningitis is 92% and the positive rate of serum is 75%, while the positive rate of serum in non-meningitis patients is 20% to 50%. It can be used for serum, cerebrospinal fluid, pleural fluid and bronchoalveolar lavage fluid testing. The rise and fall in antigen titer may also indicate efficacy, course and prognosis. If the antigen titer does not change or rises, it is a reaction to worsening disease and poor prognosis, and if the antigen titer fluctuates, it is indicative of recurrent disease. After the disease has healed, if the antigen appears again several times in serological tests with potency of 1:8 or more, the possibility of relapse should be considered. It is noteworthy that immunocompetent individuals have a lower rate of antigen positivity than immunodeficient individuals, and if immunocompetent individuals are positive it is indicative of extrapulmonary dissemination [1].
3. molecular biology detection: PCR technique has been used for fungal detection and research since 1990, and is considered one of the best methods for fungal detection because of its good specificity and sensitivity. However, PCR technology can only determine whether there is fungus in the specimen, not whether it is pathogenic or contaminating, live or dead, nor whether it is drug-resistant, so it cannot be used as a judge of efficacy and a complete substitute for traditional fungal culture methods. Therefore, it is best to do fungal culture and PCR at the same time, if the two results are consistent, then the diagnosis is clear; if not, then the test can be repeated. PCR has the greatest advantage of positive fungal culture for clinical specimens to identify the species and drug susceptibility testing, and then select the most effective antifungal drugs important basis.
4. Diagnosis: The key to the diagnosis of this disease is for clinicians to be more vigilant about the disease. ①Confirmation of diagnosis based on: surgical excision specimens, various invasive puncture biopsies to obtain histopathological evidence; blood and sterile cavity fluids (such as pleural fluid, cerebrospinal fluid) direct microscopy or positive culture of Cryptococcus. ② Clinical diagnosis based on: combined with medical history, respiratory symptoms and chest imaging evidence, while qualified sputum or bronchoalveolar lavage fluid direct microscopy or culture positive for Cryptococcus neoformans, or blood and pleural fluid specimens positive for cryptococcal podococcal polysaccharide antigen; because the cryptococcal cell wall does not have 1-3 ß-D dextran antigen, the serum G test is negative in cryptococcal infection. (iii) If only host risk factors are present without clinical symptoms and pathogenic examination support, the case is a proposed diagnosis [5].
VII. Treatment
1. pharmacological treatment: the treatment of cryptococcosis often must be based on the different immune function status of the patient and the choice of different therapeutic drugs, the first choice is diphenomycin B. The overall is the use of combination therapy, and the use of flucytosine alone is not recommended. The main drug therapy is a combination of diphenhydramine B and 5-fluorocytosine, or other antifungal drugs.
The treatment of pulmonary cryptococcosis often varies according to the severity of symptoms and immune function status, as shown in Table 1. Immunologically unimpaired patients with only focal pulmonary involvement, confirmed normal cerebrospinal fluid parameters, negative cerebrospinal fluid and urine cultures, no other extrapulmonary tissue lesions, and no symptoms may not require treatment, but must be closely monitored for changes. In the absence of meningitis but with respiratory symptoms, different therapeutic drugs are used depending on the severity of the symptoms. Renal and hematologic function must be checked before and during drug administration. In severe pulmonary cryptococcosis it is appropriate to use treatment of cryptococcal meningitis, initial combination therapy (amphotericin B + 5-fluorocytosine) followed by maintenance therapy with fluconazole has significant advantages over single drug therapy. The principles of diagnosis and treatment of invasive pulmonary fungal infections developed in China recommend the use of diamphotericin B in combination with flucytosine or fluconazole for disseminated pulmonary cryptococcosis; itraconazole can also be chosen for non-AIDS patients without meningitis. Refractory pulmonary cryptococcosis can be treated with voriconazole [6].
Patients with AIDS often have a poor response to treatment. However, initial treatment with diphenhydramine B and flucytosine is still recommended and maintained for at least 2 weeks, followed by oral fluconazole (200-400 mg/d). AIDS patients with cryptococcosis who started treatment with fluconazole died earlier than those with dicloxacillin B. Most cases relapse after treatment is stopped, so long-term suppressive therapy is needed, preferably with fluconazole 200-400 mg/d orally. Weekly intravenous diphenomycin B may also prevent recurrence. Larger doses of fluconazole are being tried and may have better efficacy. In principle, non-AIDS patients should be maintained for at least another 2 weeks after culture conversion before discontinuing treatment.
The optimal dose and duration of fluconazole for the treatment of cryptococcal meningitis in patients without AIDS has yet to be determined. Itraconazole 200-400 mg/d orally for more than 2 months has also been used successfully for maintenance or full treatment of cryptococcal meningitis. For central nervous system cryptococcosis, if the disease is serious, or if intravenous injection is not effective, intrathecal or intracerebellar medullary pool administration can be used, with the first dose of 0.05 mg to 0.1 mg of diclofenac B, plus 2-5 mg of dexamethasone. injected with cerebrospinal fluid repeatedly diluted to avoid serious consequences such as lower limb paralysis due to drug irritation. Later, the dose is increased to 1mg each time as the high limit. Intrathecal administration can generally be given once every other day or twice a week, and a total amount of 20mg is appropriate. Intrathecal administration should be cautious in cases of increased intracranial pressure and optic papilloedema [1].
2.Other therapies.
(1) Surgical therapy: limited lesions such as skin, chest granulomas and abscesses, or pulmonary granulomas and cavities can be considered for surgical excision in the absence of combined central nervous system cryptococcosis. The main surgical options are standard open-heart surgery and thoracoscopic surgery. Treatment with drugs such as diphenhydramine B or fluconazole is required both before and after surgery to control cryptococcal infection. Open thoracotomy of the diseased tissue (partial or complete lobe resection) has been shown to be effective in curing isolated pulmonary nodules. Currently, surgical treatment is not recommended except for tumor-like damage. It has been reported in the literature that patients with surgically resected pulmonary cryptococcosis without postoperative antifungal therapy are prone to develop cryptococcal meningitis after 1 year. Therefore, in pulmonary cryptococcosis, adequate doses and courses of systemic antifungal medication should be given after surgery to avoid conversion to cryptococcal meningitis [1]. Fluconazole 200 mg/d intravenously for 7 d; then fluconazole 200-400 mg/d orally for 6-12 months.
(2) Other drugs: In addition, hydroxydiamidazol, actidione (Cycloheximide), etc. can also be used to treat visceral cryptococcosis. Sulfanilamide and potassium iodide can be used as adjuvant therapy.
References
1. Cao Ehong. Pulmonary cryptococcosis. Zhao Beilei, Shi Yi, and Sang Hong, eds. Modern pulmonary fungal pathology. Beijing: People’s Military Medical Press, 2004: 134-143.
2. Jarvis JN, Harrison TS. Pulmonary cryptococcosis, Semin Respir Crit Care
Med, 2008,29(2): 141-150.
3. Hung MS, Tsai YH, Lee CH, et al. Pulmonary cryptococcosis: Clinical,
Pulmonary cryptococcosis: clinical, radiographical and serological markers of dissemination,
2008,13:247-251.
4. Kishi K, Homma S, Kurosaki A, et al. Clinical features and
high-resolution CT findings of pulmonary cryptococcosis in non-AIDS patients.
Respir Med, 2006,100: 807-812.
5. Wu B, Liu H, Huang J,et al. Pulmonary cryptococcosis in non-AIDS
patients.
Clin Invest Med, 2009,32:E70-77.
6. Pasqualotto AC, Denning DW. New and emerging treatments for fungal infections.
J Antimicrob Chemother, 2008,61:i19-i30.