The speech therapist at my last assignment had a sheet posted listing not only descriptions of speech itself, but that of abnormal speech patterns. (this was a neuro unit) It was soooo helpful. Maybe your ST can give you something similar to use as a resource.
If in doubt, I just describe the speech as best I can and quote examples. One that had me stumped was a patient who was admitted because
of a sudden change in speech and talked just like Elmer Fudd. Or Lili Von Shtupp from Blazing Saddles ["A wed wose, how womantic. "]
I kid you not... I couldn't think of any other way to describe it (no, I didn't chart elmer fudd lol... but it was tempting). I ended up googling 'elmer fudd speech impediment' (or something like that) and found out there IS a designation for that type of speech and pattern. (rhotacism)