Generalized solar lentigines in a patient with a history of radon exposure.

A woman with generalized lentigines without associated non-cutaneous abnormalities is described. The patient showed brownish-pigmented flat or slightly elevated spots with a diameter of 1–5 mm. The histopathology of the lesions was compatible with a diagnosis of solar lentigines (SLs) or flat seborrhoeic keratosis. Unlike SLs, which develop typically on sun-damaged skin of the face, the dorsum of the hands and forearms, this patient showed the lentigines most prominently on the thighs and lower legs. Besides increased recreational UV exposure, the patient had a history of occupational radon exposure in a spa with radon-containing water. Genetic analysis identified a p.S249C FGFR3 hotspot mutation in 1 lesion, supporting the diagnosis of SLs. It remains elusive whether the occupational exposure to radon-containing water in addition to the recreational UV light exposure caused the unusual distribution of the SLs in this patient.