Have you evaluated a cat for a head tilt, nystagmus, and some vestibular ataxia recently? If so, you may have seen a cat with intracranial complications from otitis media/interna (OMI). “That’s not possible!” you say, “This cat did not have a history of prior otitis and their tympanic membrane looked fine!” First, great job doing an otic exam on a cat. Secondly, according to a study of 19 cats with intracranial complications from OMI, 63% of the cases did not have a prior history of OMI and over half of the cats lacked evidence of middle ear disease on otoscopic examination. Let’s dig into that study.
This was a multicenter retrospective study published in 2019 (DOI: 10.1177/1098612X18764582) that evaluated 19 cats who were diagnosed with intracranial complications from OMI. In this report, 15 cats received a lesion localization of central vestibular disease, and 3 cats were diagnosed with peripheral vestibular signs. Only 6 cats (33%) had evidence of Horner’s syndrome and NONE of the cats had evidence of facial nerve paralysis. Remembering neuroanatomy, the facial nerve and the ophthalmic branch of the sympathetic nerve course through the ventral bulla, which is the middle ear. It is interesting that so few cats had evidence of disease in the bulla, but it also tracks with what we typically see on clinical evaluation.
There were some interesting CT and MRI findings that you can read about in the paper. All of these cats except 1 were noted to have intracranial extension of the ear disease. The 1 cat without cross sectional imaging evidence had evidence of a neutrophilic pleocytosis on CSF analysis. Speaking of CSF analysis, 10 cats had a CSF analysis performed, and all 10 cases had a neutrophilic cell dominance, but not all of them had a pleocytosis.
Cultures were submitted on 21 samples from 18 cats. The most common source was fluid from the myringotomy or ventral bulla osteotomy (VBO) and the most common bacteria isolated was Pasteurella (n=4). Pasteurella is often found in the nasal cavity of cats. This suggests that the bacterial infection can occur through eustachian tube access rather than through the external ear.
Treatment
The treatment was surgical (VBO) in 12 cats and medical in 6 cats. Medical management included myringotomy in 3 cats. All cats except 1 were prescribed antibiotics, and 14 cats were prescribed a short course of a steroid. Overall outcome was successful (improved or resolved signs) in 14 cats (74%), and unsuccessful (static, declined or euthanized) in 5 cats (26%). A successful outcome was recorded for 83% of cats that underwent VBO and 66% for those managed medically.
Key points:
1. Do not discount the option of intracranial spread of OMI in cats based on examination alone. Consider advanced imaging (MRI) for any cat with signs of central or peripheral vestibular disease.
2. Consider Pasteurella when choosing antibiotics. Amoxiclav should be successful against this organism.
3. Cats, unlike dogs, do not always show signs of facial nerve paralysis or Horner’s syndrome with OMI.
This article came across my radar because of a recent case of extension of OMI in a cat. The article is a little bit older, but I think it was worth revisiting. Hope you enjoyed this week’s TidBit Tuesday! I look forward to working with you soon!
References: Journal of Feline Medicine and Surgery; 2019, Vol. 21(2) 148–155