Amuse with mirth when suffering aches and pains (10)

I believe the answer is:

rheumatism

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'aches and pains' is the definition.
I can't tell whether this definition defines the answer.

'amuse with mirth when suffering' is the wordplay.
'with' says to put letters next to each other.
'when suffering' is an anagram indicator.
'amuse'+'mirth'='amusemirth'
'amusemirth' anagrammed gives 'RHEUMATISM'.

Can you help me to learn more?

(Other definitions for rheumatism that I've seen before include "Joint affliction" , "Inflammation of the joints" , "ailment" .)

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