PSOM (primary secretory otitis media)

 Primary secretory otitis media (PSOM) is a little understood condition in cavaliers, similar to 'glue ear' in children. It is sometimes referred to as 'middle ear disease'. Some recent studies indicate that it appears to be quite prevalent in cavaliers and the mucus plugs regularly show up on MRIs of cavaliers. It is not clear if the condition has any connection to SM, but most researchers currently think it does not. It can cause deafness, but there are other causes of deafness, too.
However, PSOM does create some of the same symptoms as SM, ranging from scratching and head-shaking to (in severe cases) seizures and neurological effects (though, given the frequency that PSOM turns up in SM-affected cavaliers, it isn't clear from the article below - one of the only ones on PSOM - whether the dogs in question might have also had SM, with SM and not PSOM the cause of the more severe symptoms). PSOM should be considered in a dog exhibiting SM-like symptoms and should be investigated in dogs showing signs of deafness, though note that neurologists say air scratching is not generally associated with PSOM. Note that very few vets (or neurologists) are familiar with PSOM or its association with cavaliers.
* You can read a recent article from the CKCSC Bulletin on one cavalier owner's experience with PSOM and an SM diagnosis here (thanks to Betsey Lynch for granting permission to include it):

The Trouble With Trouble

* A new study on PSOM in cavaliers is underway at Ohio State University by Dr Lynette Cole and a description of the study as well as an information sheet on PSOM is available here, from the Cavalier Charitable Trust. Dr Cole currently is looking for participants.

Below is the abstract from a 2003 article on PSOM in cavaliers; it can be purchased and downloaded from the link provided. It is an academic article but understandable to a general reader:
Primary secretory otitis media in the Cavalier King Charles spaniel: a review of 61 cases
Authors: Stern-Bertholtz W.; Sjostrom L.; Wallin Hoekanson N.
 Source: The Journal of Small Animal Practice, Volume 44, Number 6, 30 June 2003, pp. 253-256(4)
Publisher: BVA Publications
Sixty-one episodes of primary secretory otitis media (PSOM) were diagnosed in 43 Cavalier King Charles spaniels over a 10-year period. The principal findings were signs of moderate to severe pain localised to the head or cervical area, and/or neurological signs. Diagnosis was made by examination of the tympanic membrane and middle ear with the aid of an operating microscope under general anaesthesia. A bulging, but intact, tympanic membrane was found in most cases. Following myringotomy, a highly viscous mucus plug was found filling the middle ear. Treatment, consisting of removal of the mucus plug, flushing of the middle ear, and local and systemic medical therapy, had to be repeated between one and five times. The prognosis was good in all cases. PSOM is an important differential diagnosis in Cavalier King Charles spaniels with signs of pain involving the head and neck, and/or neurological signs.
The full article is available for purchase online here at $12.95.