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].