My cats too thin...

Question
I have a male neutered cat, approximatly 10 years old. He is an indoor cat, who is up-to-date on all his shots. His problem (and ours!) is that he likes to sneak out when someone leaves the door open too long (We nicknamed him, Houdini). The longest he had ever been away from us was 3 days, until recently. He got out and had been missing for FOUR weeks! We just got a call this morning, someone found him, read the tag on his collar (REWARD-My phone#), and called us. I ran down to get him. Gave the finder a small reward and thanked them very much. My question is; How can I fatten him up? He lost a lot of weight due to poor diet and lack of food. He appears healthy in most other ways except for a small laceration on the bottom of his right front paw, which does not appear to be infected, once we cleaned it and examined it. We will watch him for obvious signs of ill health due to his month long adventure, but what kinds of high caloric foods would you recommend to increase his weight? We normally feed each of our cats 1/2 a can of wet food such as nine-lives, plus a bowl of dry food that is available all day long to them and of course fresh water, changed at least once a day..

Answer
I would definitely call your vet to get some deworming medication as it is likely that he picked up parasites while on his adventure scavenging for food.  A stool sample should also be analyzed after the deworming to make sure he doesn't have any residual parasites.

I would try feeding him canned IAMS KITTEN food three times a day in addition to your dry food.  If he doesn't gain any weight in a few weeks, take him to the vet for some blood tests to check kidney, liver, thyroid and blood sugar.