Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for your cat. Certainly stress can exacerbate or trigger problems in feline patients (and canine ones for that matter) but there's usually more going on than just stress.
There are actually several possible explanations for his behavior in a cat this age:
1. Feline Asthma which is similar to this condition in a human in that there is inflammation in the lungs which is triggered by something in the environment such as pollens, smoke, aerosol sprays, etc. It's not often easy to identify the trigger, though.
This is often a difficult diagnosis to make. Chest x-rays might be suggestive as would bloodwork (eosinophils might be elevated but they aren't in every case). If I suspect this condition, then I'll sometimes treat my patients with steroids. If they are 100% better, then this is the diagnosis in my opinion until proven otherwise. It may seem like a crude way to diagnose this condition, but if I rule out other possible reasons for the signs first (see below) then I don't worry about side effects from steroids.
2. Infectious conditions such as Bordetella or Mycoplasma could cause coughing in a cat but, again, are somewhat challenging to diagnose. If I'm uncertain as to whether or not this might be the problem, then I'll dispense Doxycycline 5 mg/kg twice a day This drug has the added benefit of anti-inflammatory properties which can be of benefit for some patients.
3. Lung worm which is a parasite that is most often diagnosed with a fecal sample This condition would be much less likely in an inside cat. One effective treatment would be panacur.
4. Heartworm disease although he's a little on the younger side for such a condition. This disease is transmitted by mosquitoes and depending on where you live, may be a possibility. We do have a test for this condition which is often done in a vet's office. Unfortunately, we don't have an effective treatment for it in cats. This disease is different in a cat than in a dog and the coughing is related to inflammation in the lungs.
Steroids can be used to treat this inflammation.
Cats can develop a condition known as heartworm associated respiratory disease (HARD) which can result in significant damage to the lungs and resultant symptoms such as wheezing and compromised respiratory function. These cats are typically negative when an antigen test is done but often positive when an antibody test is run. Ultrasound is normal with no worms detected. Radiographic changes are usually detectable helping with the diagnosis but you have to know what you're looking for since those changes could be confused with changes secondary to lung worm or migrating rounds worms or possibly asthma.
Unfortunately, we don't have effective treatments for this condition either although steroids can be effective in helping to reduce inflammation and the accompanying symptoms.
5. Heart disease. These cats usually have other signs in addition to coughing such as weight loss or exercise intolerance so this also seems less likely. But I wanted to at least mention it since stress might trigger a worsening of the condition. A chest x-ray can be useful in determining if there is an enlarged heart or fluid in the chest but ultrasound is usually needed to determine the exact diagnosis.
6. There are other conditions that might cause a cat to cough such as pneumonia but those cats are really sick.
7. Upper respiratory infections are at the bottom of this list for a reason. These cats are usually sneezing and have discharge from the eyes and/or nose. Stress can trigger an episode if a chronic condition and acute ones can be seen if the cats go outside
If this were my case, I would:
1. Take a chest x-ray if not already done.
2. Evaluate a fecal sample and run a heartworm test.
3. Consider ultrasound if the heart needs further evaluation.
4. Treat with steroids and monitor response. In some cases if for whatever reason an x-ray is not done, I'll treat with steroids anyway. If they improve, the condition was asthma or inflammation. If they don't, then something else is going on and further testing needs to be done. In my opinion, the potential benefit would be worth the small risks involved in terms of any possible side effects.
My only caution is that I try to rule out an upper respiratory infection as best I can; steroids will reduce the immune system and make this condition worse. It's not life threateningly worse, but the symptoms are more intense.
I hope this helps. Deb