I agree, this is pretty vague. But, for the Symptom of "weakness," there is the R53 Code Set for Malaise and Fatigue, with some Exclusions. But R Codes should not be use for "diagnosis" codes unless there is no identifiable specific disease code. As for Muscular Weakness, there is Code Set M62: Other Disorders of Muscle, the most specific is M62.81: Generalized Muscle Weakness.
I don't know whether this helps you much at all
Respectfully submitted, Alan Pechacek, M.D.
icd10orthooder.com