Fungal diseases caused by species of the genus Cryptococcus are a growing public health problem, with the species belonging to the Cryptococcus neoformans and Cryptococcus gattii complexes being the most common and studied. In recent years, other species belonging to related genera have emerged, including Naganishia diffluens. As there are few reports on this species, it is important to emphasize its significance, particularly given that it has been found in skin lesions in immunocompromised patients, as in the case presented here. This highlights the importance of paying due attention to this species and recognizing its clinical relevance.
Case reportA 27-year-old male patient with a diagnosis of acute promyelocytic leukemia M3 (APL M3) experienced a febrile episode with skin lesions compatible with fungal infection, coinciding with marked neutropenia and the start of chemotherapy. Mycological analysis of skin lesions allowed the isolation of a fungus that was identified as N. diffluens.
ConclusionsThe increase in the frequency of N. diffluens infections can be attributed to the rising number of patients with risk factors. The use of new microbial identification tools, such as molecular biology, which made it possible to accurately identify the causative agent, is highlighted.
Las enfermedades fúngicas causadas por el género Cryptococcus representan un problema de salud pública que se ha incrementado en los últimos años. Las especies más comunes y estudiadas pertenecen a los complejos Cryptococcus neoformans y Cryptococcus gattii. Sin embargo, recientemente han surgido otras especies de géneros relacionados, como Naganishia diffluens. Existe poca información sobre N. diffluens. Es crucial destacar su relevancia, especialmente por la posibilidad de ser aislada de lesiones cutáneas en pacientes inmunosuprimidos. El caso que presentamos destaca la importancia de realizar un atento análisis micológico al entender el rol clínico de esta especie.
Caso clínicoUn paciente de sexo masculino de 27 años con diagnóstico de leucemia aguda promielocítica M3 (LAP M3) presentó un episodio febril y lesiones cutáneas compatibles con infección fúngica. Esto coincidió con una marcada neutropenia y el inicio de quimioterapia. El análisis micológico de las lesiones cutáneas permitió aislar un hongo que se identificó como N. diffluens.
ConclusionesEl aumento de las infecciones causadas por N. diffluens puede atribuirse al creciente número de pacientes con factores de riesgo. Destacamos el uso de nuevas herramientas de identificación microbiana, como la biología molecular, que permiten una identificación precisa del agente causal.
Fungal infections caused by species of the genus Cryptococcus are a growing public health concern. While species of Cryptococcus neoformans and Cryptococcus gattii complexes are the most common and well-studied, other less frequent species have emerged in recent years as causative agents of infections.5 Clinical information on the diseases caused by these atypical pathogens is mainly dispersed in sporadic case reports. Despite their lower frequency, these species pose diagnostic and therapeutic challenges due to the difficulty of their diagnosis by conventional methods and the lack of sufficient evidence to establish treatment guidelines for these rare species.
Naganishia diffluens was initially included within the genus Cryptococcus, but subsequent molecular studies revealed that this species exhibits distinctive genetic and phenotypic features that differentiate it from other species of Cryptococcus. Consequently, in 2015, Naganishia was proposed as a new genus to house N. diffluens and other related species.1
Globally, there are few reports on this species. It is crucial to highlight its relevance, especially considering it can potentially appear in skin lesions often confused with tinea.4,9 Its isolation is more common in immunocompromised patients,5 as in the case presented, which highlights the importance of giving it due attention and clinical relevance.
Case reportA 27-year-old male with no significant medical history was admitted to treat Vincent's angina, which was unresponsive to amoxicillin–clavulanate therapy. A complete blood count and bone marrow biopsy revealed an acute promyelocytic leukemia (APL, M3). The patient presented with fever and oropharyngeal lesions with bleeding, suggesting an underlying infection. He was hospitalized and received empirical treatment with piperacillin–tazobactam and amikacin for 13 days. BD BACTEC™ Plus Aerobic/F (Aero) blood cultures were negative. Subsequently, the patient underwent chemotherapy according to the AIDA protocol. Induction phase was successful, resulting in a favorable hematological response. During the treatment, the patient experienced febrile neutropenia along with acneiform pustular and papular lesions, which evolved to pustules and subsequently developed a central crust (Fig. 1).
A skin biopsy was performed and sent to the Mycology laboratory. Direct examination revealed encapsulated yeast cells (Fig. 2a), and cream-colored smooth colonies (Fig. 2b) grew in the cultures. In the microscopic analysis of the fungus obtained in culture, encapsulated yeast cells without pseudohyphae were observed; the isolate tested positive for urease activity. These characteristics are consistent with the Cryptococcus genus.
Initial attempts to identify the fungal isolate using the VITEK™ system (bioMérieux, Inc., Hazelwood, MO) resulted in misidentification as Cryptococcus albidosimilis with low discriminatory score (35% probability). Subsequent identification using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS; MALDI Biotyper™ ver. 9.0.0.0; Bruker Daltonics, Billerica, MA, USA) identified the strain as N. diffluens with a score of 1.89 as the best match, and a score of 1.77 as the second-best match. The result was reported as N. diffluens (Cryptococcus diffluens)/Naganishia albidosimilis (C. albidosimilis) due to MALDI-TOF MS's inability to accurately differentiate between these species.8 Sequence analysis of the ITS regions and the D1/D2 domain of 26S of the rDNA showed both 100% identity to the type strain N. diffluens CBS160. The strain was deposited in the Mycology Reference Center Culture Collection (Faculty of Biochemical and Pharmaceutical Sciences, National University of Rosario) with the accession number CCC 217-2024. The ITS and 26S sequences were deposited in the GenBank database under accession numbers PX092653 and PX092666, respectively.
An empirical treatment consisting of liposomal amphotericin B at a dose of 3mg/kg/day for 4 weeks was prescribed. The antifungal treatment continued afterwards with isavuconazole, starting with a loading dose of 200 mg every 8h for 48h, followed by a maintenance dose of 200mg on a daily basis. This treatment proved to be effective.
DiscussionWhile dermatophytes, Candida, and Malassezia remain the primary agents of skin fungal infections, immunocompromised individuals are at risk for infections by a broader range of fungi. This includes species closely related to Cryptococcus, some of which were previously classified within that genus. For example, a recent rise in infections due to these species, such as Naganishia albida and Papiliotrema laurentii (formerly Cryptococcus laurentii) has been described.5
Although N. diffluens is a rare cause of disease, a few cases have been reported in the literature. To the best of our knowledge, only three cases have been documented worldwide to date. The first case involved a young, otherwise healthy male patient, who presented with erythematous, crusted, non-painful nodular lesions on the wrist and arm.3 This fungus was later identified as the cause of a superficial infection characterized by annular, erythematous, and scaly patches localized in both axillae and the trunk of a patient with cirrhosis.4 Additionally, N. diffluens was isolated from a diabetic patient who exhibited clinical features consistent with tinea cruris.9 This fungus has also been found colonizing the skin of patients with atopic dermatitis.7,10 It is noteworthy that N. diffluens has been isolated from skin only, but other rare Cryptoccocus-related species have been found in other sites of the human body.5
The genus Naganishia includes yeasts that are encapsulated, globose or elliptical, variable in size, and typically do not have hyphae or pseudohyphae.5 Taxonomically, they belong to the Tremellomycetes lineage within the subphylum Agaricomycotina of the phylum Basidiomycota.2 In a recent reclassification five main clades within the order Filobasidiales were described: aerius, albidus, cylindricus, filobasidium, and gastricus. The albidus clade, for its part, houses 17 species, including N. diffluens (formerly known as C. diffluens).1
Accurate identification of N. diffluens is essential due to its morphological and histopathological resemblance to C. neoformans; this species also shares antigenic factors with Cryptococcus species.4 Differentiation between the two entities can be achieved using the phenol oxidase test, which is negative in N. diffluens. The inability of most rare Cryptococcus species to grow at temperatures of 35–37°C is another difference.5N. diffluens has been misidentified using the ID 32™ and VITEK™ systems.5,6 These examples underscore the limitations of biochemical methods for accurate species identification. DNA sequence analysis of both the ITS regions and D1/D2 domain of 26S rDNA, as performed here and in previous studies, provides a more reliable identification.3,4,9
The reclassification of N. diffluens has significant implications in the infection diagnosis and the management of the patient. The increasing prevalence of rare Cryptococcus infections can be attributed to a growing number of patients with risk factors and the advancements in medical technology that prolong the lives of patients with comorbidities. Additionally, it is essential to acknowledge the pivotal role of molecular biology in accurate microbial identification.
Although the combination of amphotericin B and flucytosine is the preferred treatment for cryptococcosis, the management of superficial infections caused by N. diffluens remains undefined. Interpretive guidelines and susceptibility breakpoints for Cryptococcus susceptibility testing are yet to be established by the Clinical & Laboratory Standards Institute. Previously reported clinical cases achieved successful treatment with terbinafine,9 itraconazole,4 and a combination of oral itraconazole and topical isoconazole.9 In the case presented here, the patient was successfully treated with a combination of liposomal amphotericin B and isavuconazole. Delving into antifungal susceptibility studies is crucial to establish breakpoints that will guide prompt and effective treatment decisions, especially considering that species within this genus, such as other basidiomycetes, are refractory to echinocandin therapy.
The implementation of reporting systems for the occurrence of these mycoses is fundamental to comprehend their true global impact. Progress in defining more rapid and efficient diagnostic techniques is pivotal for the accurate identification and diagnosis of these infections.
Ethical statementDuring the preparation of this work, the authors utilized Gemini 2.0 Flash to enhance the English writing. Following the use of this tool, the authors reviewed and edited the content as necessary and assume full responsibility for the published content.
