Back to veterinary medicine. A big, friendly, middle-aged, black lab was presented to me the other day with an "eye problem."
Indeed his left eye was affected but the problem was not of the eye per se, but rather of the sympathetic innervation to the
eye(s).
Heh?
Let me illustrate: If I scared the s--t out of you, your sympathetic nervous system would kick in. Your heart would start to race, your blood vessels in your muscles dilate to allow more oxygen to reach them, your eyes pop out a little, your eyes (lids) are wide open, and your pupils are dilated - all for "fight or flight."
Forgetting all but the eyes, Horner's syndrome involves a disruption of the sympathetic innervation to the eye(s). So what ensues? This dog had a droopy eyelid, a constricted (or miotic) pupil, a sunken eyeball and a mildly-protruded third eyelid (we don't have that one).
Ok, that was the easy part. A syndrome is not a disease but rather a constellation of clinical symptoms that results from a disease. My job is to find out what is causing this dog's Horner's syndrome.
Many of these cases are idiopathic. That is to say, there is no discernible cause to the disease. Most resolve by themselves. This is somewhat comforting. Another important place to look is the middle ear, through which a portion of the sympathetic branch runs. Dogs with a middle ear infection often have Horner's syndrome. Other causes include spinal diseases such as a "pinched nerve" from a disk, or a spinal tumor. Even hypothyroidism (low thyroid function) can cause Horner's. This guy's thyroid is normal. So far, it looks idiopathic as I cannot find a cause. I took x-rays of the tiny spherical bones at the base of the skull (called tympanic bullae) as these may show evidence of a middle infection. I've sent those radiographs to be interpreted by a specialist in radiology.
The good news is that this dog has no clue he has Horner's. He's happy as a clam.
A cat with Horner's syndrome. Note the third eyelid protruding (the cat's right eye).
