Chronic kidney disease (CKD) should not be a cause of leg weakness. Stage 4 CKD is commonly associated with weight loss and loss of appetite which can lead to muscle wasting. However, inactivity alone can also do this. The longer he is inactive, the more loss of muscle strength can be expected. I am unable to make a specific diagnosis based on the information that you present. I can only suggest that he continue to consult with his physician.
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