CT Confirmed: Diagnosing PSOM in CKCS Requires More Than Otoscopy

Diagnosis of Primary Secretory Otitis Media in the Cavalier King Charles Spaniel

Lynette K. Cole, Valerie F. Samii, Susan O. Wagner, Päivi J. Rajala-Schultz

Background:
Primary secretory otitis media (PSOM) is a middle ear disease predominantly observed in Cavalier King Charles Spaniels (CKCS), often misdiagnosed or overlooked due to overlapping clinical signs with other disorders such as syringomyelia. Historically, diagnosis has relied on the identification of a bulging tympanic membrane and mucus accumulation post-myringotomy. This study aimed to assess the diagnostic utility of otoscopy, tympanometry, pneumotoscopy, and tympanic bulla ultrasonography, using computed tomography (CT) as the gold standard for detecting PSOM in CKCSs with compatible clinical signs.

Methods:
Sixty CKCSs with clinical signs suggestive of PSOM underwent otoscopy, CT, tympanometry, pneumotoscopy, and tympanic bulla ultrasonography under general anesthesia. Dogs with CT-confirmed middle ear soft tissue density underwent myringotomy and middle ear flushing. The sensitivity and specificity of each diagnostic test were calculated using CT as the reference standard. Clinical and neurologic signs were documented, and response to flushing was evaluated postoperatively.

Results:
PSOM was diagnosed in 43 of 60 dogs (72%) via CT. A large bulging pars flaccida was 100% specific but only 29% sensitive for PSOM. Tympanometry showed the highest sensitivity (84%) but low specificity (47%), while pneumotoscopy had moderate sensitivity (75%) and specificity (79%). Bulla ultrasonography yielded 67% sensitivity and 47% specificity. Clinical signs such as hearing loss (72%), neck scratching or pruritic ears (72%), and head shaking (28%) were common. Neurological exams revealed cervical pain in 95% of PSOM cases, though owners reported it less frequently. After myringotomy and flushing, 71% of affected dogs showed clinical improvement, particularly in hearing.

Limitations:
Only CKCSs with suggestive clinical signs were included, limiting applicability to asymptomatic dogs. Imaging and procedural variability, small tympanic bullae in CKCSs, and the potential for mucus redistribution during procedures may have affected diagnostic accuracy. MRI was not performed to exclude syringomyelia, limiting differentiation of overlapping signs.

Conclusions:
A bulging pars flaccida is a specific indicator of PSOM in CKCSs, but its absence does not rule out disease. When the pars flaccida is flat, none of the evaluated diagnostic tools (other than CT) offer sufficient sensitivity and specificity to replace CT. Therefore, CT imaging remains essential for confirming PSOM in CKCSs with compatible clinical signs but equivocal otoscopic findings.

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