Hello, and welcome to FDMB
Do you actually mean that he is "limping" or are you seeing back leg weakness?
Diabetic neuropathy is a common cause of back leg weakness in diabetic cats, especially those with high blood glucose levels.
Some of us have found that supplementing with methyl B12 (methylcobalamin) helps the recovery. 'Zobaline' is a popular brand of methly B12 that is made especially for cats and is easily available in the US (you can also buy it from outside the US but it can be expensive to import, depending on where you live). There are other brands available also.
Getting the cat into a better blood glucose range helps
a lot. How are Milo's blood glucose levels?
Low potassium can also be a cause of back leg weakness. You would need your vet to do a blood test to determine any deficiency. If the potassium is low it can be supplemented.
"Limping" could have a number of causes. Has it come on suddenly? Could Milo have suffered an injury to his leg or his foot? Is there any swelling anywhere?
Could he have arthritis?
As you say, it sounds like a vet visit is needed....
Do let us know what happens. And feel free to ask any other questions you want to.
Would you like to tell us more about Milo, for example: When was he diagnosed? What insulin is he on, and what is he eating at the moment?
Eliz