Hello and thanks for researching this very important question!
Strokes, as such, are assumed to be rare in pet cats, but are beginning to be diagnosed more with MRI scans...these are performed under general anesthesia, so many older pets are not healthy enough to be tested.
A number of things can cause a disturbance of the "vestibular" system in the brain, which is responsible for balance, among other things. These conditions include:
1) ear infection, dogs and cats have VERY long ear canals, so a deep-down exam in needed to diagnose this properly,
3) contamination of the brain with waste products usually handled by young healthy kidneys and liver...cats develop kidney and liver disease to a fairly high degree as they age,
4) generalized infections (like Toxoplasmosis) that can travel into the brain. There is such a thing as "Idiopathic Vestibular Syndrome"...(idiopathic--pathology which doesn't make sense)...which does not have a cause that we can find. This is more common in middle-aged and older pets. The most severe symptoms fade (or become adjusted to!) over the course of a few weeks, and the most prominent thing we see is the head-tilt...looks weird, but is not a serious problem long-term.
The chance of more severe problems increases with increased age of your cat.
Symptoms of vestibular disturbance include rapid eye movement from side-to-side, inability to stand or walk due to dizziness, nausea and/or vomit (with refusal or inability to eat), spastic head movements, and a tilt in the orientation of the head. Affected cats prefer to lie on one side of the body only.
The time that you mentioned he was feeling sickly was probably linked with the start-up of whatever has caused this neurologic imbalance. Non-specific symptoms that preceed acute illness are often referred to as an "aura".
Since he has stopped improving on the medications, some more testing would be in order to try and find out if he is having an illness in some other part of his body. High fever can adversely affect the entire brain...blood tests are needed to evaluate him for diabetes, hyperthyroid, kidney or liver disease, etc. Treatment and prognosis depends entirely on what is found, and what degree of organ damage you may be dealing with.
If nothing of this nature is found, then he may indeed have a small brain tumor that is beginning to press out on more vital locations. It is not possible to predict how quickly this may progress to preventing him from getting along at home.
You do need to have him re-checked as soon as you can arrange it, but in the meantime, you might consider confining him to a small warm room where he will be able to rest and not be in danger from stairs or opening doors. Keep liquified food and clean water near him, and cover the floor with a thick quilt so that any eliminations are easy to clean up. These patients feel worse in the pitch dark, so a night-light bulb is helpful during nighttime hours.
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