Mucoid cysts develop subcutaneously over the distal interphalangeal joint and may be adjacent to the nail, producing abnormalities of growth. These cysts develop as an extension of the synovial membrane and are linked to the joint by a fine tract. Very careful excision is required for a cure.
Naevi may occur adjacent to the nail and a benign melanocytic naevus can produce a pigmented streak. Subungual melanoma may produce considerable pigmentation of the nail and often causes pigmentation of the cuticle, so called Hutchinson's sign. Sometimes subungual melanoma is amelanotic so there is no pigmentary changes and any rapidly growing soft tumour should raise suspicions of this condition.
Subungual exostosis can cause a painful lesion under the nail. It is confirmed by x ray examinations.
Glomus tumours arise as tender nodules.
Periungual fibrokeratomas also develop in patients with tuberous sclerosis.
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