Diagnosis and treatment of the otitis externa and media

Abstract

Left-sided facial nerve paralysis with the clinical signs of muzzle deviation to the right, poor control of the tongue, left ear droop, ptosis of left upper eyelid, reduction in tear production and superficial focal corneal ulceration in the left eye in this 13-year-old Appaloosa gelding are typical complications of otitis media (Edgington et al., 2023). Based on these clinical findings, the likely cause is an acute neuritis of the facial nerve induced by otitis externa with subsequent otitis media. The pathogenesis of the otitis externa and otitis media is determined by the anatomical and histological structure of the ear. The anatomical-specimens (Figure 1) show the close proximity of facial nerve and osseus external ear canal including tympanic cavity of the middle ear. The facial nerve (VII) is only separated by a very thin layer of mucosa between the canalis facialis and tympanic cavity proper of the middle ear (Blanke et al., 2014a) (Figure 2). A different diagnostic approach compared to the investigations of the gelding in the accompanying Case Report is described in the following case. A 7-year-old Arabian mare with right head tilt, poor mastication, with muzzle deviation to the left, right ear droop, ptosis of right upper eyelid, reduction in tear production and keratitis sicca of the right eye had these endoscopic abnormalities in the right guttural pouch and right osseous external ear canal which are shown in Figure 3. The cellular and ceruminal material and exudate which obstructed the right osseous external ear canal were removed using foreign body forceps via the endoscope. Based on the exudation in the osseous external ear canal, this exudate was removed frequently by soaking up the fluid with small cotton balls which were inserted into the osseous external ear canal using the foreign body forceps of the endoscope (7 mm) every 3–4 days over a period of 4 weeks. Staphylococcus aureus was cultured from the exudate of the right osseous external ear canal collected with a sterile cotton ball using foreign body forceps. Based on the investigation, otitis externa purulenta of the osseous external ear canal and inflammation of the temporohyoid articulation and stylohyoid were diagnosed, with facial nerve paralysis and vestibular syndrome (right head tilt) as complications (Blanke et al., 2014b). The otitis externa purulenta induced otitis media which caused the acute neuritis of cranial nerve VII with the clinical signs of facial nerve paralysis. The otitis externa purulenta generated an osteopathy of the osseous external ear canal including the processus styloideus, enlarged tympanohyoideum and stylohyoideum. The internal ear was involved too because the mare had a right head tilt which was caused by the diseased vestibular system of the internal ear. Based on the antibiogram, enrofloxacin was used at a dosage of 5 mg/kg bwt q 24 h orally and flunixin meglumine 1.1 mg/kg bwt q 24 h orally over 4 weeks. The keratitis sicca was treated with carbomer eye drops three times a day. After 4 weeks of these treatments, a full recovery was achieved (Figure 4). The right head tilt recovered after 6 months. The mucopurulent exudate which drained out of the created opening of the tympanic bulla was seen in the medial compartment of the left guttural pouch of the 13-year-old Appaloosa gelding. This bacterial (Pseudomonas aeruginosa) induced mucopurulent exudate filled in the whole tympanic cavity proper and the epitympanic recess of the middle ear and caused an otitis media purulenta sinister (Edgington et al., 2023). The facial nerve in the canalis facialis is only separated by a thin layer of mucosa from the tympanic cavity proper of the middle ear. Based on this, the facial nerve was inflamed and a neuritis occurred. The acute neuritis of the facial nerve reduced the motor nerve function that led to the muzzle deviation to the right, left ear droop and ptosis of left upper eyelid. The decreased parasympathetic function of the involved left facial nerve reduced the tear production of the glandula lacrimalis which induced the corneal ulcer. The clinical signs of the 13-year-old Appaloosa gelding and the 7-year-old Arabian mare are similar. The diagnostic procedures of the gelding included CT imaging of the head, and after opening the tympanic bulla of the middle ear using a laser via the endoscope in the medial compartment of the sinister guttural pouch, a mucopurulent exudate drained out which led to the diagnosis of a bacterial induced otitis media exudativa (purulenta) (Edgington et al., 2023). However, the diagnostic procedures of the mare only included endoscopy of the external ear canals and the guttural pouches including the collection of the exudate from the right osseous external ear canal. These led to a diagnosis of bacterial induced otitis externa purulenta which involved the middle and internal ear too. Based on our findings in horses with these described clinical signs, otitis externa secondary to temporohyoid osteoarthropathy was diagnosed. Otitis externa and media was not caused in these horses by guttural pouch empyema (Streptococcus equi subsp. equi) because an exudate in the osseous external ear canal could not be verified endoscopically. The opening between the middle ear and the guttural pouch called the ostium tympanicum tubae auditivae must be so tight that blood or exudate of the guttural pouch cannot drain into the tympanic cavity of the middle ear. However, the bacterial induced exudate of external ear canal causes inflammatory infiltration of the surrounding epithelium, tympanic membrane, bone, middle ear structures, facial nerve and through the fenestra vestibuli and fenestra cochleae into the internal ear. The cellular and ceruminal debris of the cartilaginous and osseous external ear canal containing the skin microbiota, sweat, dust, bleeding in the cartilaginous external ear canal induced by blood sucking mosquitos or parasites are risk factors which can cause inflammation and exudation in the epithelium of the osseous external ear canal with extension into the middle and internal ears (Schusser, 2015). Endoscopy of the external ear canals and guttural pouches is helpful in horses with the above-described clinical signs. This is important for both diagnosis and treatment. The external ear canal should also be endoscopically investigated in horses with behavioural changesbecause these horses could have a bilateral or unilateral ear canal obstruction or thickened epithelium which cause hearing deficit or deafness (Schusser et al., 2020). No conflicts of interest have been declared. Not required for this clinical commentary. Open Access funding enabled and organized by Projekt DEAL.