Diagnosis: Pili Annulati

The spangled appearance of hair under reflected light with alternate parallel banding under polarized microscopy favors the diagnosis of pili annulati. Association with atopy has not been reported in the literature according to my knowledge.

Discussion

Pili annulati is an extremely rare non-fragile hair shaft disorder characterized by banding leading to spangled hair. It is an autosomal dominant condition with a recently identified genetic locus on Chromosome 12. ^[1] Although it is clinically detectable in blond or lightly pigmented hair as speckled banding, it is only an incidental finding because of the non-fragility of hair. ^[2] It is difficult to diagnose this condition in dark hair since the banding is obscured by the pigment. The characteristic spangled appearance of hair with reflected light is the only clue in dark hair.

An inherent defect in the hair shaft leads to formation of air-filled cavities within the cortex that lie parallel to the long axis of the hair. ^[3] These are seen in the polarized microscopy as alternating light and dark bands. Examination of hair under electron microscopy shows cobble-stoning of the cuticle and air-filled cavities within the cortical cells and between the keratin macro fibrils.

Pili annulati has to be differentiated from pseudo pili annulati which is sometimes the feature of normal hair due to an optical illusion caused by partial twisting. Pili annulati differs from trichothiodystrophy which shows alternating light and dark bands arranged perpendicular to the long axis of the hair shaft resembling tiger's tail [Table 1].

Pili annulati is rarely associated with woolly hair, anhidrotic ectodermal dysplasia, ^[4] blue nevi ^[5] and alopecia areata. ^[6] Association with atopy is extremely rare. Since atopic children might have various hair shaft disorders it is worth studying a large population of atopic children for hair shaft abnormalities.

Pili annulati does not resolve spontaneously or improve with age. Since hairs are non-fragile no treatment is required.