A case of pigmentary hair naevus (Becker).

: A healthy 14-year-old Norwegian male developed a typical Becker's naevus on the left shoulder and upper scapular region, about six months after an intracutaneous BCG-vaccination in the homolateral junction of the shoulder and upper arm. The evolution of the lesion had been modified by exposure to sunlight during the following six years, with partial fading of the hyperpigmentation. Biopsies taken from the centre and from the edge of the lesion at the age of 19 years showed the usual histological picture seen in cases of Becker's naevus, but focal areas within the periphery showed a chronic granulomatous infiltrate of lupoid pattern in the dermis, mainly follicular and perifollicular in distribution. Acid-fast bacilli were not demonstrable in the sections, and in culture no tubercle bacilli were isolated from a central and histologically non-specific site. The implications of the histological findings are discussed, stressing the possibility that Becker's naevus may be a form of cutaneous tuberculosis caused by BCG or other mycobacteria of low virulence, precipitated by ultraviolet light and possibly modified by immunological factors.