Hello and welcome to JustAnswer. My name is ***** ***** I am a registered veterinary surgeon.
I am sorry to hear Schroedinger is losing fur. Luckily he isn't in a box! ;-)
The first common reason cats lose fur is due to flea bite reaction. They typically loose fur due to over-active grooming. The best way to rule this out is to use an effective flea treatment/prevention: e.g. fipronil (frontline). In addition to using a flea treatment, you should use a larvacide. Unfortunately, the only approved larvacides are prescription only medication, and you will need to be seen by your regular veterinary surgeon.
Other possible common causes for loss of fur on the abdomen and the legs are: allergies, mites, fungus, ring worm (a different type of fungus). An examination and a few test by your veterinary surgeon can test for these issues.
Less common causes for grooming in these areas are: Pain associated with bladder stones/crystals, pain associated with arthritis, and feline pancreatitis. Finally, there are some endocrine (hormonal) causes of fur loss. These can be tested for by your regular veterinary surgeon.
The most common non-medically related problem is pyschogenic, typically stress. If all other medical problems have been examined and ruled out, then this is the most likely cause. This website has some very good information on behavioural problems in cats: http://www.merckmanuals.com/vet/behavior/normal_social_behavior_and_behavioral_problems_of_domestic_animals/behavioral_problems_of_cats.html
In short, Schroedinger should be seen by your regular veterinary surgeon to rule out medical causes, the first being flea bite hypersensitivity.
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