Discussion:
Mucormycosis is a rare fungal infection caused by filamentous fungi belonging to the class Zycomycetes, in the order of Mucorales. They are not very virulent in immunocompetent patients [1]. They become pathogenic in immunocompromised patients such as those with diabetes and acidosis, immune deficiency with neutropenia, severe malnutrition and during corticosteroid or cytotoxic treatments [2,3,4].
The rhino-orbito-cerebral localization is the most frequent (40% of cases) [5]. Other locations have been reported, including cutaneous, pulmonary, disseminated, gastrointestinal and miscellaneous [6]. For the otologic location, several hypotheses have been suggested: either a passage of the fungal spores from the sinonasal cavities to the middle ear via the eustachian tube, or their penetration to the middle ear through a perforation of the tympanic membrane, or an auricular mucormycosis invading the middle ear and the mastoid [7,8] as in our case.
Clinically, otologic mucormycosis may manifest as refractory otitis externa involving the pinna and external auditory canal giving a blackish necrotic appearance with skin scaling [8]. It may be presented as a middle ear cholesteatoma with foul-smelling otorrhea and otalgia [4,6,9]. Endocranial or skull base extension indicates a severe infection with cranial nerve damage, with or without neurological signs. The particularity of our observation consists of the auricular cutaneous starting point with involvement of the external ear and the large extension to the parotid, retro auricular and temporal regions. This extension was accompanied by bacterial superinfection with parotid abscess extending to the parapharyngeal space associated with peripheral facial and vagus nerve paralysis. Among the cranial nerves, the facial nerve is the most commonly affected in auricular mucormycosis [7,8,9,10]. Vagus nerve involvement, presumably related to this parapharyngeal extension, is however unusual and would probably be the first case of this type to be reported so far.
Reviewing previously described otologic mucormycosis within the literature, only a few cases of auricular mucormycosis have been reported in the literature. Indeed, Aljehani M [11] reported in 2021 a case of an 18-month-old girl with undiagnosed diabetes presented with an aggressive form of auricular mucormycosis with facial nerve palsy that have fully recovered after a combination of antifungal, antibiotic, and antiviral with extensive surgical debridement. Kumar and Nishan [8] reported in 2015 a case of a mucormycosis of the external ear invading the temporal bone with associated facial palsy. The patient had surgical debridement with a modified radical mastoidectomy and facial nerve decompression combined with systemic liposomal amphotericin B. The patient full recovered with a significant improvement in facial palsy after surgery. M Faruk Oktay [7] reported a case of a 17-year-old female patient with diabetic ketoacidosis presented with auricular mucormycosis and of the external ear canal. Unfortunately, the patient died on the seventh day despite of the extensive debridement associated with systemic amphotericin B.
The diagnosis of mucormycosis is based on histopathological examination. Direct mycological examination is rarely positive, and culture on Sabouraud agar is often negative [2]. Pathological examination shows broad mycelial filaments 7-10 microns wide and 100-200 microns long, hyaline, non-septate with right-angled branching [2, 5].
Treatment consists of a combination of antifungal (amphotericin B at high doses of 5-15mg/ kg/day), surgical debridement and systematic control of comorbidities [5,8]. Resection of necrotic tissue reduces the fungal load and improves the penetration of antifungal agents into infected areas [12]. Due to the rarity of cases, the duration of antifungal treatment for otologic mucormycosis has not been established. Various studies have shown the favorable role of hyperbaric oxygen therapy. Increased oxygenation of the affected tissue improves the phagocytic capacity of neutrophils and decreases local acidosis [13]. In addition, high oxygen levels inhibit fungal spore germination and mycelial growth in vitro.
In terms of prognosis, the mortality of otologic mucormycosis is significantly lower than that of the rhino-orbito-cerebral form [9]. This may be explained by the poor vascularity of the middle ear compared to the paranasal sinuses limiting angioinvasion and spread of infection, differences in the microbiome between the middle ear and paranasal sinuses or simply a reflection of the small number of cases [8].