Non-mycotic onychopathies account for ca 50% of deformaties of the nails and their knowledge is therefore important for the differential diagnosis of onychomycoses. Most difficulties are caused by those cases where a non-mycotic onychopathy combines with a secondary mycotic infection. The authors describe a female patient with onychomycosis on the feet confirmed by laboratory tests and changes on he thumbs, which at first by their clinical appearance also suggested onychomycosis. Only the difference in the response to systemic treatment with itraconazole (4 pulses) when the toe nails healed while the nails on the hands remained short and fringed drew attention to the different etiology. An X-ray of the thumbs revealed shorter last phalangi. The patient admitted that the nails of the thumbs were shorter and broader since birth, however only in recent years they thickened and became discolored.

        Key words: onychomycoses - differential diagnosis - brachyonychia