Primary secretory otitis media ("PSOM") is a canine condition that you may have heard referred to as "Glue Ear." This condition can affect not only dogs, particularly Cavalier King Charles Spaniels and other brachycephalic (short-nosed) breeds, but people and some other animals as well.
In sample studies funded in part by the ACKCSC Charitable Trust, the sample study indicated 40% of the study group had PSOM.
PSOM is an inflammatory condition of the middle ear. The dog’s middle ear becomes blocked with a gooey plug of mucus. If it builds up, the tympanic membrane can begin to bulge, causing pain. The root cause of PSOM is unknown, as is the reason it affects some dogs and not others, but one belief is that it could be due to a flaw in the functioning of the of the normal processes of the Eustachian tube, which is part of the middle ear, causing either inadequate normal drainage of the middle ear through the nose, or increased production of mucous by the eustachian tube, or both.
PSOM can affect only one ear, or both. As the fluid increases/remains in the middle ear, it thickens and hardens, causing a thick, viscous mucous "plug" to form. This plug will continue to increase in size and can cause loss of hearing, balance, coordination and/or pain. Its symptoms often mimic that of another disease that can affect the Cavalier, which is Syringomyelia ("SM").
While PSOM affects other short-nosed (brachycephalic) breeds, it seems to affect Cavaliers on a more frequent basis. In Cavaliers, the condition may be hereditary, but as of yet, there’s no definitive evidence of a genetic component other than its frequency in the breed.
The brachycephalic nature of the Cavalier's head means that the space within the muzzle of the dog is shorter than in other breeds. All the same structures exist, but are compressed, including all the various airways and drainage channels inside of it. The ears, nose and throat are normally already closely connected to each other in both spacing and functioning, but in short-nosed dogs, the shorter muzzle can also impact the shape and positioning of these structures, especially where the eustachian tube drains into the nose. Head shape and size, as well as the lush, long ears could also play a part in this.
Clinical signs of PSOM may or may not be presented (non-presentation is referred to as "sub-clinical"). If clinical signs are present, you should always have your dog examined by a vet. As mentioned previously, many of the symptoms can mimic other problems. But some of the symptoms you might notice are:
In severe cases, PSOM may be visible via radiograph or even when the veterinarian takes a look with an otoscope. Your vet will need to perform a physical examination to rule out things like ear mites, ear infections or other problems. Other times, diagnosis may require a CT or MRI scan. It is possible your vet may need to perform some more in-depth diagnostic tests, such as x-ray examination, or image scans of your dog’s head and ears. Your dog may need to be referred to a veterinary specialist who has access to the necessary machinery.
Several options are available as treatment; your vet can help you choose the best option for your own dog. But generally, treatment involves removing the mucus plug and flushing the middle ear (a procedure called a myringotomy), followed by medication with corticosteroids and antibiotics.
In less severe cases there are some medications that can help thin the mucous, sometimes helping it to thin out enough to drain naturally.
In more severe or stubborn cases, surgical intervention may be needed, which usually takes the form of a surgery called a myringotomy. This procedure is performed under general anaesthesia, wherein a small cut into the eardrum is made to remove the plug and flush out the eustachian tube.
An alternative approach to this is to perform a ventral bulla osteotomy, which permits the vet to again drain the Eustachian tube and remove the plug of mucous, but involves making the entry incision in the neck rather than the ear itself.
Unfortunately, recurrence of the plug is not uncommon, and dogs affected by PSOM may need treatment to be repeated more than once before it’s successful, but generally PSOM has a good prognosis.