Recently Nationwide insurance released data on the most common medical conditions based on 1.3 million pet insurance claims in over 550,000 pets. It's an interesting list.
Dogs
1. Allergic dermatitis
Average cost: $210
2. Otitis externa (ear infection)
Average cost: $153 per dog
Average cost: $153 per dog
3. Benign skin neoplasia (cancer)
Average cost: $348 per dog
Average cost: $348 per dog
4. Pyoderma and/or hot spot
Average cost: $122 per dog
Average cost: $122 per dog
5. Osteoarthritis
Average cost: $299 per dog
Average cost: $299 per dog
6. Periodontitis/dental disease
Average cost: $312 per dog
Average cost: $312 per dog
7. Gastropathy (stomach problems)
Average cost: $279 per dog
Average cost: $279 per dog
8. Enteropathy (intestinal problems)
Average cost: $139 per dog
Average cost: $139 per dog
9. Cystitis or urinary tract infection
Average cost: $284 per dog
Average cost: $284 per dog
10. Soft tissue trauma
Average cost: $229 per dog
Average cost: $229 per dog
Cats
1. Feline cystitis, or FLUTD (lower urinary tract disease)
Average cost: $441 per cat
Average cost: $441 per cat
2. Periodontitis/Dental disease
Average cost: $326 per cat
Average cost: $326 per cat
3. Chronic renal disease
Average cost: $628 per cat
Average cost: $628 per cat
4. Gastropathy
Average cost: $313 per cat
Average cost: $313 per cat
5. Hyperthyroidism
Average cost: $396 per cat
Average cost: $396 per cat
6. Enteropathy
Average cost: $189 per cat
Average cost: $189 per cat
7. Diabetes mellitus
Average cost: $862 per cat
Average cost: $862 per cat
8. Upper respiratory infection
Average cost: $185 per cat
Average cost: $185 per cat
9. Allergic dermatitis
Average cost: $158 per cat
Average cost: $158 per cat
10. Inflammatory bowel disease
`Average cost: $311 per cat
Overall I would agree with these lists, though I don't see hyperthyroidism or diabetes in cats as commonly as reported here. I would also put dental disease higher on the list for dogs. But these lists are also a bit skewed considering that the vast majority of American pets are not on any form of insurance, so this may not be a completely representative population despite the absolutely huge sample size.
I notice that there are several preventable diseases on this list. Dental disease can be completely prevented and controlled with the proper care. Most stomach and intestinal disorders come from eating things that the pet shouldn't, which can be at least somewhat controlled by the owners. Most cases of diabetes in cats happen with obesity, which is preventable if the owners are careful about what and how they feed. Chronic skin and ear problems in dogs are definitely difficult to manage and can get expensive, but it is possible to do so. We could certainly change these lists quite a bit with proper preventative health care in pets.