I Don’t Know Why: Idiopathic Disease

"Idiopathic" sounds so definitive. Sadly it ain’t necessarily so

January 18, 2016 (published)
By Anne Elizabeth Katherman, DVM, MS, DACVIM/Neurology

Idiopathic, a name that rolls off the tongue of the veterinarian with a lovely feel of reflecting all the time and money that was spent achieving the volume of knowledge that accompanies the DVM degree.

It sounds so definitive, so scientific. Sadly it ain’t necessarily so. The medical term idiopathic comes from Greek roots: idios, or "one's own," and pathos, "suffering" or "disease." Appropriate really because idiopathic as defined by Merriam and Webster means: “arising spontaneously or from an obscure or unknown cause,” which is why those of us who use the term suffer so much. It requires a confession that we don’t know the cause of the problem,, and for a medical professional that is a very hard thing to admit.

In my own little niche of the veterinary world, that of veterinary neurology, we run across a lot of idiopathic diseases and actually give these diseases official names: idiopathic facial paralysis, idiopathic head tremors, and idiopathic vestibular syndrome, to mention a few.

Translated into normal English, German, Transylvanian or Greek etc. idiopathic facial paralysis means “I don’t know why your dog/cat can’t move his facial muscles,” idiopathic head tremors means “I don’t know why your dog has a head tremor,” idiopathic vestibular syndrome means, yes, you’ve got the hang of it, “I don’t know why your dog/cat has a head tilt.”

So what do these idiopathic diseases look like? Let’s start with idiopathic facial paralysis. One day your dog looks at you and you notice a drooping of an upper lip or in some cases both upper lips. Because the dog can’t move his lips, water and food may spill out of the mouth when he’s eating. There may also be an inability to close his eye(s), which can result in a secondary ulcer if a piece of dust gets into the eye, and in some cases there is an inability to move the ear(s). Otherwise your pet will be healthy and happy.

In the case of idiopathic vestibular syndrome, also known as “old dog vestibular syndrome” and “feline vestibular syndrome,” your pet may develop a sudden, severe head tilt and may roll over and over and over again to the same side. In addition, you or your veterinarian may notice a rapid movement of both eyes from side to side. We call this horizontal nystagmus. If your pet can walk at all, she may look like she’s been on an alcoholic binge. Vomiting is common, as it is in people who get on carnival rides that go round and round and round again. It is due to the same cause, too: a disturbance of the vestibular system, the system of balance within the ear.

Idiopathic head tremors are most common in certain breeds of dogs, the English bulldog, the Doberman, the boxer and the Labrador being the poster puppies for this problem. These dogs look like one of the sports figure bobble heads, but in some cases the head may move up and down in a “yes” fashion and in other dogs the head may move from side to side in a “no” fashion. Unlike dogs with seizures there is no loss of consciousness and the dog is otherwise completely normal. Cats seem to be spared this problem so if your cat develops a head tremor, more serious conditions need to be considered.

The good news is that with idiopathic facial paralysis and idiopathic vestibular syndrome, the problem usually resolves over time without specific treatment. However, with idiopathic facial paralysis, lubricating the eye to prevent ulceration is indicated; with idiopathic vestibular disease, which causes vertigo and hence nausea, drugs to prevent vomiting may be helpful. Idiopathic head tremors don’t improve but they don’t get worse and they don’t seem to bother the patient. So no news is good news and actually worth paying for, despite the fact that I have just told you that not only do we not know the cause of these diseases, but treatment usually isn’t necessary or helpful.

Before deciding that a visit to the veterinarian is wasted because, according to Dr. Google the signs your pet is showing correspond to an “idiopathic” disease, remember that clinical signs often do not limit themselves to a single disease. This is especially true for neurological diseases where the clinical signs correspond very well to the location of the problem within the nervous system (brain, spinal cord, peripheral nerves, and cranial nerves) but not to a specific diagnosis. Hence a head tilt may be due to idiopathic vestibular disease or to an inner ear infection, a brain tumor, or other diseases. Inability to move the upper lip(s) may be due to idiopathic facial paralysis, a nerve sheath tumor, hypothyroidism, or middle ear infection, etc. Head tremors may be due to idiopathic head tremors, intoxication, abnormal development of the cerebellum or problems with nerve insulation etc.

How can we tell the difference?

Here is where the knowledge that your veterinarian paid so dearly to gain and you are paying so dearly to access comes in and why it is worth paying for their opinion. By taking a thorough history from you regarding the development and progression of clinical signs, and performing a comprehensive physical and (in my area of expertise) neurological examination, the veterinarian can determine how likely it is that your pet has an idiopathic disease or whether more diagnostic testing is indicated to exclude the possibility of other more serious conditions that may benefit from primary treatment.

So if after examining your pet, your veterinarian tells you that the problem is likely idiopathic, don’t feel as if you have wasted your time and money, since in most cases some wicked bad diseases have just been ruled out. It’s a little like the difference between picking your own stock investments at random versus consulting a stockbroker. You may be lucky, but if you aren’t is it worth the risk?

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