pencil-in-cup sign

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pencil-in-cup sign

A term of art referring to bony erosions in which the narrowed end of a metacarpal or phalange rests in the expanded end of the adjacent bone sharing the joint. The pencil-in-cup sign is classically described in atrophic neuropathic arthropathy of severe psoriasis, as well as in rheumatoid arthropathy.

Imaging
Plain films of involved joints show a tapering of the convexity and an exaggeration of the concavity of bones in the joint, and are accompanied by osteoporosis.