Discussion
This case of fatal, progressive, invasive, pulmonary aspergillosis demonstrates several important factors in the treatment of patients with this disease. Treatment failure usually relates to any of 4 possible factors: host immune status, severity or burden of disease, appropriate dosing of antifungal agents, and drug resistance. This patient’s immune system was heavily suppressed for a prolonged period. Attempts at reducing immunosuppression to the minimal required dosage to prevent a GVHD flare were unsuccessful and became an unmodifiable risk factor, a major contributor to his demise.
The risks of continuous high-dose immunosuppression in steroid-refractory GVHD is well understood and has been previously demonstrated to have up to 50% 4-year nonrelapse mortality, mainly due to overwhelming bacterial, viral, and fungal infections.4 All attempts should be made to cease or reduce immunosuppression in the setting of a severe infection, although this is sometimes impossible as in this case.
The patient’s disease burden was significant as evidenced by the bilateral, multifocal pulmonary nodules seen on chest imaging and the disseminated disease found at postmortem examination. His initial improvement in symptoms with voriconazole and the evolution of his images (with many of his initial pulmonary nodules becoming pneumatoceles) suggested a temporary positive immune response. The authors believe that the Rhizopus in his sputum represents noninvasive colonization of one of his pneumatoceles, because postmortem examination failed to reveal Rhizopus at any other location.
Voriconazole has excellent pulmonary and central nervous system penetration: In this patient serum levels were well within the therapeutic range. His peculiar drug resistance pattern (sensitivity to azoles and resistance to amphotericin) is unusual. Azole resistance in leukemia and patients with HSCT is more common than is amphotericin resistance, with current estimates of azole resistance close to 5%, ranging between 1% and 30%.5,6 Widespread use of antifungal prophylaxis with azoles likely selects for azole resistance.6
Despite this concern of azole resistance, current IDSA guidelines recommend against routine susceptibility testing of Aspergillus to azole therapy because of the current lack of consensus between the European Committee on Antibiotic Susceptibility Testing and Clinical and Laboratory Standards Institute on break points for resistance patterns.3,7 This is an area of emerging research, and proposed cut points for declaration of resistance do exist in the literature even if not globally agreed on.8
Combination antifungal therapy is an option for treatment in cases of possible drug resistance. Nonetheless, a recent randomized, double-blind, placebo-controlled, multicenter trial comparing voriconazole monotherapy with the combination of voriconazole and anidulafungin failed to demonstrate an overall mortality benefit in the primary analysis, although secondary analysis showed a mortality benefit with combination therapy in patients at highest risk for death.9
Despite the lack of unified standards with susceptibility testing, it may be reasonable to perform such tests in patients with demonstrating progressive disease. In this patient’s case, amphotericin B was added to treat the Rhizopus species found in his sputum, and while not the combination studied in the previously mentioned study, the drug should have provided an additional active agent for Aspergillus should this patient have had azole resistance.
Surprisingly, subsequent testing demonstrated the Aspergillus species to be resistant to amphotericin B. De novo amphotericin B-resistant A fumigates is extremely rare, with an expected incidence of 1% or less.10 The authors believe the patient may have demonstrated induction of amphotericin-B resistance through activation of fungal stress pathways by prior treatment with voriconazole. This has been demonstrated in vitro and should be considered should combination salvage therapy be required for the treatment of a refractory Aspergillus infection especially if patients have received prior treatment with voriconazole.11
