Disseminated Trichosporonosis with Trichosporon asahii

ARTICLE

The basidiomycetes yeast Trichosporon is the causative agent of white piedra, a superficial cutaneous infection endemic in tropical and subtropical regions [1]. Over the past decade, invasive infection with Trichosporon has been recognized more frequently in immunocompromised patients. Neutropenic patients with acute leukemia or those undergoing bone marrow transplantation are most often affected [1-3].

Recently, Guého et al. [4] revised the genus Trichosporon using morphology, ultrastructure, physiology, ubiquinone systems, DNA/DNA reassociations and 26S ribosomal RNA partial sequences. Only one strain was T. cutaneum, even though 12 strains were named T. cutaneum by the current method of diagnosis.

We describe a case of invasive infection with T. asahii in a patient with acute myeloblastic leukemia (AML).

Case

A 53-year-old man with acute myeloblastic leukemia (M2) was examined because of red papules on his trunk and extremities in October 1997. In September 1997, he was admitted to the department of internal medicine of our hospital for the treatment of AML. Induction therapy was started with idarubicin hydrochloride (12 mg/m² for 3 days) and cytarabine hydrochloride (100 mg/m² for 10 days). He had developed agranulocytosis since September 19 and became febrile after 4 days. Red papules appeared on the trunk and extremities on October 3, 1997. The white blood cell count was 100/mm³, with 0% of neutrophils. The C-reactive protein level was 26.0 mg/ml.

On physical examination, the patient was found to have several dark red papules with white centers scattered on his upper extremities, chest wall, abdomen, and thighs (Fig. 1).

Biopsy of a papule on the abdomen showed fungi arranged in a radial star burst pattern in the dermis and only a slight cellular inflammatory reaction. The fungus consisted of slender septate hyphae, small arthroconidia and blastoconidia, when stained with periodic acid-Schiff and Grocott-Gomori methenamine-silver stains. The fungus invaded dermal blood vessels and erector muscles (Fig. 2).

Multiple serial blood cultures yielded yeast that was identified as Trichosporon species. The patient was put on intravenous amphotericin B (20 mg/day) and fluconazole (200 mg/day), but his condition progressively deteriorated and he died 5 days later.

Mycological examination

A culture on Sabouraud's glucose agar of a skin lesion specimen produced cream-colored, yeast-like colonies within seven days. The colonies were wrinkled, folded, glabrous with a brush border (Fig. 3). Microscopic examination revealed the presence of true hyphae, blastoconidia and arthroconidia typical of Trichosporon species. The isolate assimilated glucose, sucrose, maltose, lactose, galactose, and L-arabinose, whereas it did not assimilate sorbitol and inositol. It grew at 37 °C and was susceptible to 0.1% cycloheximide. We examined the isolate with the polymerase chain reaction-based approach according to previously reported methods [5]. Briefly, the primers that would specifically amplify only T. asahii, were TAAF (forward; 5'-GGATCATTAGTGATTGCCTTTATA-3') and pITS4 (reverse; 5'-TCCTCCGCTTATTGATATG-3'). The primers amplified the DNA from the isolate, and produced a 500 bp fragment as shown (Fig. 4). Therefore, this isolate was identified as T. asahii.

Susceptibility testing of the isolate to amphotericin B, flucytosine, and fluconazole, performed by using the National Committee for Control Laboratory standard methodology [6] modified for microdilution technique, revealed minimal inhibitory concentrations (MICs) at 6.25 mg/ml, 12.5 mg/ml, and 6.25 mg/ml, respectively.

Discussion

Trichosporon is a natural inhabitant of soil and occasionally constitutes a part of the normal flora of human skin. It also colonizes the throat and lower gastrointestinal tract. The fungus is classically associated with superficial infections, most notably white piedra. More recently, it has been recognized as an opportunistic pathogen that can cause potentially fatal systemic infection in immunocompromised hosts [1].

Guého et al. [4] revised the taxonomy of the genus Trichosporon on the basis of morphological and biochemical properties, co-enzyme Q systems, DNA relatedness, and partial 26s rRNA sequences. We used the name T. cutaneum instead of T. beigelii on the basis of the statement by Guého et al. that the name T. beigelii is of doubtful validity. It has been pointed out that the taxon T. cutaneum represents a heterogeneous species based on various criteria. Only one strain was named T. cutaneum by the current method of diagnosis. Guého et al. [7] described the genus Trichosporon as containing six human pathogenic species: T. asahii, T. asteroides, T. cutaneum, T. inkin, T. mucoides, and T. ovoides. Of the six species, T. mucoides and T. inkin are the main causative agents of white pieda. T. cutaneum and T. asteroides are isolated from superficial cutaneous infections. T. asahii is a major causative agent of disseminated trichosporonosis. Several techniques for the identification of Trichosporon species have been reported. Guého et al. [7] mentioned that the six pathogenic species were clearly differentiated by several key characteristics: a combination of assimilation of carbon compounds, cycloheximide resistance, and the ability to grow at 37° C. On the other hand, Sugita et al. [5] reported that they developed species-specific primers for T. asahii based on the sequences of the internal transcribed spacer regions. The Trichosporon species isolated from our patient was identified as T. asahii according to physiological methods and PCR.

The clinical picture of disseminated trichosporonosis consists of pneumonia, hepatitis, encephalitis and septicemia. These features often develop even when a granulocytopenic patient is receiving amphotericin B empirically for a fever that is unresponsive to antibacterial agents [1, 8]. Trichosporon is isolated mainly from blood, sputum, urine, skin and faeces. Factors that may predispose a patient to disseminated infection include cytotoxic chemotherapy-induced granulocytopenia, corticosteroids, prosthetic valve surgery, hemochromatosis [1] and aquired immunodeficiency syndrome [9, 10].

Cutaneous involvement occurs in approximately 30% of patients with trichosporonosis [1]. The lesions are usually purpuric papules and nodules with central necrosis or ulceration [1, 10-13]. Culture of these lesions grow Trichosporon and biopsy specimens demonstrate histopathologically hyphae, arthroconidia and blastoconidia often invading dermal blood vessels [13, 14]. Although the microscopic appearance may easily be confused with Candida or Aspergillus, close histological observation should reveal pseudohyphae, numerous rectangular arthroconidia and a few blastoconidia which can lead to the correct diagnosis [1, 13].

The prognosis of trichosporonosis is poor and most often fatal. Some strains of Trichosporon may be susceptible in vitro to amphotericin B, while other strains may have borderline or complete resistance to amphotericin B. Infection may disseminate to various organs and be difficult to treat even when the standard antifungal agent amphotericin B is utilized. There has been controversy over the treatment of trichosporonosis. Walsh et al. [1] demonstrated that some strains of T. beigelii were inhibited, but not killed by safely achievable concentrations of amphotericin B in serum. Tashiro et al. [15] and Perparim et al. [16] demonstrated that the azoles, miconazole and itraconazole, had higher in vitro activity than amphotericin B. However, in vitro susceptibility tests have not been standardized and the results do not always correlate with clinical response. Anaissie et al. [17] suggested that antifungal azoles were an effective therapy for Trichosporon infection. Walsh et al. [18] reported that fluconazole was the most active azole and that miconazole had no in vivo activity against disseminated trichosporonosis. The results of treatment have been very poor, largely due to the advanced nature of the underlying illness, and the resolution of infection in leukemic patients with neutropenia is related primarily to bone marrow recovery following remission of leukemia.

Trichosporonosis remains a rare infection, even though the number of immunosuppressed patients has increased. Knowledge of this organism as a potential pathogen, especially in the appropriate clinical setting, i.e. in neutropenic patients, will lead to early recognition of this serious infection.

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