My cat has just developed a black discharge in one ear. Ive never seen or heard of this kind of thing before. I have taken him to my veterinarian twice, and on each occasion, she cleaned the ear and microscopically examined the discharge. Im assured that there are no ear mites present. Whats the reason for the discharge and whats the prognosis?
The black discharge in your cats ear is likely the result of a condition called otitis externa, a medical term which, simply defined, means inflammation of the external ear canal, the L-shaped cartilage tube that extends from the outer opening of the ear all the way down to the eardrum.
Not surprisingly, the condition has many potential causes. In my experience, otitis externa is much more common in dogs than it is in cats, probably because of dogs frequent predisposition to allergic skin diseases, various hormonal disorders and unusual ear conformations in some breeds. But an exception is ear mite infestation in kittens. These arachnid parasites are so commonly found in kittens that Im actually surprised when I dont find them. Adult cats are much less likely to be infested with ear mites, but its always wise to check for them anyway. Your veterinarians examination of the ear gook under the microscope should have allowed her to detect them if they were present, and she probably also looked for fungi, bacteria and other parasites that can inhabit the ear and either initiate or perpetuate inflammation. Unlike ear mites, these other organisms may not be the primary cause of the problem; they could just be making things worse. Sending a sample of the discharge to a diagnostic laboratory for further evaluation can help guide treatment if a bacterial infection is highly suspected.
One ear or two?
Because it appears that just one of your kittys ears is affected, Im most suspicious of a problem localized in the ear canal itself: perhaps a foreign object, such as a blade of grass; an inflammatory polyp; or even a tumor. Your veterinarian will have to use an otoscope to thoroughly examine the entire ear canal all the way down to the eardrum to know for sure. (In fact, a thorough otoscopic examination of the ear canals is important in ALL cases of otitis.) To do so, she will need to extend the scope deep into the canal and then point it inward to see around the corner made by the 90 degree bend. Your cat may need to be sedated for this procedure, especially if the ear is already sore. Treatment will depend on whats found.
If both ears were affected, Id be more apt to consider a generalized problem. But generalized disease or localized disease can cause either just one or both ears to be involved.
When confronted with otitis externa in an adult cat, its always wise to look for an underlying problem, that is, some condition that makes the external ear susceptible to disease. Allergic skin disease can predispose otitis externa, but, unlike some allergic dogs, most allergic cats have obvious skin disease in addition to their ear problem. And some medications used to treat ear conditions paradoxically can create inflammation; in these cases, the medicine makes things worse. Disorders that hamper the immune systems ability to fight infection can lead to ear infections, too. If shes not done so already, your veterinarian should check to make sure your cat isnt infected with feline leukemia virus or feline immunodeficiency virus. Diabetes mellitus and, less commonly, Cushings disease (an excess of the adrenal hormone cortisol) can predispose a cat to skin and ear infections. However, it would be very unlikely for your cat to have either of these diseases without their causing obvious and significant problems in addition to an ear infection. Nonetheless, if no other cause were found, it would be prudent to rule out these conditions.
The prognosis depends on the cause and how well the condition responds to treatment. For example, ear mites are usually fairly easy to eradicate, and, once gone, the ear inflammation resolves. If, on the other hand, the ear disease is due to a tumor in the ear canal or a serious condition like Cushings disease, the prognosis is much poorer.