Clinical diagnosis, based on history of minor trauma and physical examination
If unclear if wound is fluctuant:
Have patient apply pressure to distal aspect of affected digit
A larger than expected area of blanching, reflecting a collection of pus, may identify need for drainage
Have patient apply pressure to distal aspect of affected digit
A larger than expected area of blanching, reflecting a collection of pus, may identify need for drainage
Paronychia
Bed bugs
Black hairy tongue
Closed fist infection 
Pellagra
Digital Mixoid Cyst 
Ataxia
Hand cellulitis