Discussion
This article describes a case of subacute pulmonary mucormycosis in a patient with recurrent DKA. Although patients with poorly controlled DM commonly present with the rhinocerebral form of mucormycosis, pulmonary involvement with a subacute course has been described. Determining the final diagnosis for the current patient was challenging due to the subtlety of his respiratory symptoms and the inconsistent initial findings on chest radiography. A pulmonary disease was finally suspected when a mass was found on the CT scan. However, the middle mediastinal mass was more suspicious for malignancy, particularly given the patient’s smoking history and persistent hyponatremia. In fact, the lack of any neoplastic findings on the initial endobronchial biopsy prompted the health care team to pursue a second biopsy that was consistent with mucormycosis.
This case demonstrates the challenges of prompt diagnosis and treatment of this potentially fatal infection. Furthermore, the extent of the disease at diagnosis precluded this patient from having a surgical intervention, which has been associated with better outcomes than those of medical management alone. Finally, it remains unknown whether the patient had an underlying malignancy, which could have increased the likelihood of pulmonary mucormycosis; the biopsy yield may have been confounded by repeated sampling of necrotic material caused by mucormycosis. Further investigation of any potential pulmonary neoplasm was limited by the patient’s clinical condition and the poor prognosis due to the extent of infection.
Mucorales is an order of fungi comprised of 6 main families that have potential to cause a variety of infections. The genera Mucor, Rhizopus, and Rhizomucor cause the majority of infections.1 Mucormycosis (infection with Mucorales) is generally a rare fungal infection with an incidence of about 500 cases per year in the U.S. However, the incidence is increasing with an aging population, higher prevalence of DM and chronic kidney disease, and a growing population of immunocompromised patients due to advances in cancer therapy and transplantation. Risk factors for pulmonary mucormycosis include conditions associated with congenital and acquired immunodeficiency: hematologic malignancies, uncontrolled DM, solid tumors, and organ transplantation.2
Presentation
Notably, there seems to be an association between specific organ system involvement and predisposing conditions. Pulmonary mucormycosis occurs much less frequently than does the rhinocerebral form in patients with DKA but occurs more commonly in patients with neutropenia that is due to chemotherapy or hematopoietic stem cell transplantation (HSCT) for the treatment of hematologic malignancies.2
The mechanisms for preferential site infection are not well understood with current knowledge of mucormycosis pathogenesis. Current research demonstrates monocytes and neutrophils may play a vital role in the body’s defense against Mucor by both phagocytosis and oxidative damage. Chemotaxis and oxidative cell lysis seem to be compromised in states of hyperglycemia and acidosis. Iron metabolism repeatedly has been shown to play a role in the pathogenesis of mucormycosis. Specifically, patients receiving deferoxamine seem to have a predisposition to Mucorales infections, presumably due to the increased iron supply to the fungus.4 Notably, systemic acidosis also facilitates higher concentrations of available serum iron.
One of the main characteristics of mucormycosis is its ability to aggressively invade blood vessels, causing thrombosis and necrosis and subsequently disseminate hematogenously or through the lymphatic system. This property, at least in large part, depends on endothelial cell damage following phagocytosis of fungus by these cells.
Of note, some of the azole class of drugs (eg, voriconazole), which may be used for antifungal prophylaxis in patients with hematologic malignancies accompanied by neutropenia, have been implicated in predisposition to mucormycosis.2 It also is commonly seen in patients undergoing HSCT. Patients with DM and DKA also can present with pulmonary mucormycosis but generally have a more indolent course unless they develop pulmonary hemorrhage.3 Infection usually occurs by inhalation.
Patients may report dyspnea, cough, and chest pain, which is sometimes accompanied by a fever. Presentation is generally indistinguishable from other causes of pneumonia, and the routinely obtained sputum cultures are usually not diagnostically significant.
Radiographic findings are variable and may include pulmonary nodules, consolidations, masses, and cavitary lesions.1 Due to tissue invasion, a CT scan of the chest might demonstrate a mass crossing mediastinal tissue planes. Definitive diagnosis requires a biopsy with a demonstration of characteristic broad-based nonseptate hyphae with tissue invasion as well as a positive culture (Figures 4 and 5).5 Due to nonspecific symptoms as well as laboratory and imaging findings, a biopsy and, therefore, definitive diagnosis are often delayed. However, postponing medical and surgical therapy for mucormycosis has been associated with worse outcomes.6 With the absence of easily available serologic tests and unspecific symptoms in early disease, many mucormycosis cases are diagnosed postmortem.