Useful link: http://www.pcds.org.uk/clinical-guidance/nails
Always consider the possibility of malignancy in a single dystrophic nail.
Please use the Advice and Guidance service for a dermatology opinion.
Always send nail samples for mycology.
Advice on collecting a sample for mycology:
Using nail clippers, samples should be taken comprising the whole thickness of the nail, as near as possible to the proximal edge of the lesion. The majority of infections start under the nail, so the subungual debris is particularly valuable. This can be removed with a scalpel or dental probe. Superficial scrapings of the nail plate are only useful in cases of superficial onychomycosis, where white crumbly patches are see on the dorsal surface of the nail or in proximal subungual onychomycosis.
Up to 50% of nails in which fungus has been seen on direct microscopy fail to grow a pathogen. Therefore if skin lesions are present in soles, toe webs or on palms please send samples from these as well, as they are probably caused by the same pathogen and are more likely to give a positive culture.(1)