Aetiology of laryngeal aspergillosis
Primary invasion of the larynx by Aspergillus is uncommon and is very rare in immunocompetent individuals. As per the literature review, till date, 38 cases of primary laryngeal aspergillosis in immunocompetent patients have been documented over 50 years. Aspergillus fumigatus was reported to be the underlying causative mould in the majority of cases, documented so far; except for two cases. A. niger infection reported by Gangopadhyay et al. from India [6] and Gallo and colleagues from Italy reported Aspergillus flavus as the etiologic agent in a patient with Felty’s syndrome [7]. In the present case a immunocompetent student had Aspergillus fumigatus responsible for the laryngeal pathology.
Disease pathogenesis
Aspergillus is a well-known opportunistic fungus causing allergic and invasive disease in immunocompromised hosts [8]. The pathogenesis of laryngeal aspergillosis in an immunocompetent host is not well understood. The Aspergillus conidia are ubiquitous in nature as the fungus grows in a saprophytic environment (soil and decaying matter), it could well be possible that exposure of heavy fungal load in air may allow the fungus colonise the dark airway cavities [3] which could favour their slow germination without any symptoms. Such colonisation of the paranasal sinuses leads to fungal ball formation [9]. Hoarseness of voice was the only symptom in this case without any other predisposing conditions like corticosteroid or systemic antibiotic therapy. This is in contrast with other reports where patients developed symptoms after being treated with corticosteroid or systemic antibiotic therapy or after vocal abuse for many years (Table 1).
Epidemiology and risk factors for developing primary laryngeal aspergillosis
Amongst the reviewed 38 reported cases 16/37 (44%) were males, and 21/37 (57%) were females. Age group ranged from 12 to 74 years. Dutta M et al. [3] reported in 2015 that 50% of immunocompetent subjects with primary laryngeal aspergillosis had no identifiable contributory factors, but 14.29% had vocal abuse and steroid intake. Smoking, broad-spectrum antibiotics and exposure to radiation was detected in 10.7% of cases. Of the cases, 7.1% had vocal fold cyst, whereas 3.6% had a history of COPD, oral sex and diabetes. Six cases have been reported between 2015 and 2017 (Table 1); three of these cases were without any identifiable risk factors. Remaining three cases (and a few documented prior to 2015) had a history of using corticosteroid inhalers for bronchial asthma, which could have led to abrogation of the local immunity in the throat or could have altered the flora of the laryngeal mucosa, allowing the overgrowth of Aspergillus [10]. The exact predisposing conditions contributing towards the disease progression in the present case remains obscure but could be multifactorial with a complex interplay between host and the environment.
Time trend and geographical distribution of primary laryngeal aspergillosis
Laryngeal aspergillosis in the immunocompetent individual, though infrequently reported, seems to be an emerging condition. Lack of definite guidelines for clinical diagnosis due to the rarity of the disease might have resulted in under-reporting in the past. As shown in Fig. 2, the incidence of primary laryngeal aspergillosis in immunocompetent patients has been steadily rising over the past ten years. It seems that there has been a higher rate of reporting of the cases, especially after the 1990s, with a steady rise in the number of cases in the past seven years (Fig. 2). As depicted in the map, (Fig. 2) most of the new cases reported (11/20,) between 2010 and 2017, were from the Indian subcontinent, followed by China (4/20). This emphasizes that possibility of primary laryngeal aspergillosis must be entertained in all cases, presenting with typical features of laryngeal inflammation along with hoarseness of voice.
Challenges in the diagnosis of laryngeal aspergillosis and utility of molecular diagnostics methods
As per the literature review, most of the laryngeal aspergillosis cases were diagnosed by the characteristic morphological features of the fungus in the biopsied material. However, result on species identification was lacking in majority of reported cases. Detection of hyphae, simulating those of Aspergillus in a biopsy specimen can be suggestive of fungal invasion but, is not necessarily pathognomonic of aspergillosis. Therefore, it becomes mandatory that the organism be isolated in pure culture and accurately identified. Few authors identified Aspergillus up to species level based on morphology and a couple of reports provided evidences of identification based on molecular methods [11, 12]. Moreover it is well known that fungal identification with conventional culture technique has its own limitations. As per the studies [13] conducted earlier, as well as in the present case, we could not successfully culture the fungus from the laryngeal biopsy. In these situations, etiological identification directly from clinical specimen via extraction of DNA and sequencing is advantageous. In this study, PCR on DNA extracted from paraffin-embedded tissue confirmed the aetiology. The extended region of the gene encoding the large ribosomal subunit (28S) of fungi was used for PCR amplification and sequencing. This region was previously explored for designing of broad range PCR primers and showed generation of successful amplicons and sequences from yeasts and filamentous fungi [14]. Because of the paucity of sequences of this extended region of fungal 28S rDNA in the public databases, the non D1/D2 region was rarely utilized for sequence-based detection and identification of fungi directly from clinical specimens. A recent study [15] showed the utility of the non D1/D2 region as a favorable target for the genus, and to a limited extent, species-level identification of pathogenic fungi in various fresh and FFPE samples. In the present study, attempt to amplify the internal transcribed spacer 1 (ITS1) region from the DNA extracted from the sample was not successful. One possible explanation might be due to the relatively larger size of the ITS1 region (~ 250–350 bp) than this non D1/D2 region (198 + _25 bp). Although accurate species identification required sequencing of at least a partial ITS region such as ITS 1 or ITS2, the non D1/D2 multicopy gene could give a satisfying genus level identification. In our study, this region could identify the genus and species of the pathogen with clear discrimination from other species of Aspergilli (with less % similarity scores) as evidenced from the BLAST hits. Therefore, this non D1/D2 region must be considered for PCR-sequencing from direct clinical specimens in those cases where partial ITS genes fail to amplify.
Treatment of cases
In majority of the reported cases, including the present one, itraconazole was used as an empiric treatment, though voriconzole is the treatment of choice against invasive apsergillosis [16]. Possibly cost of the antifungal agent is an important limiting factor during treatment of fungal infections in developing countries. The critical condition of the patient, arising out of the acute laryngeal pathology may be a compelling reason for the empiric treatment on an emergency basis, yielding invariably positive outcome following therapy. Recent reports of the global emergence of azole resistance in A. fumigatus [17] may be of concern in the management of such patients in future. Prompt species identification and detection of resistance are of paramount importance in the management of laryngeal mycosis.
Therapeutic outcome and relapse
In all 38 cases reviewed (Table 1), there was complete resolution of symptoms without any relapse, irrespective of the therapeutic modality adopted. There was not much difference in the time period between administration of antifungal drugs and relief of symptoms, regardless of whether the drug administered was itraconazole or voriconazole. Thus, considering the toxicity of conventional amphotericin B, and the cost of liposomal amphotericin B; empiric therapy with either itraconazole or voriconazole may be strongly advocated as better therapeutic options.
