Pili Annulati

Pili annulati (ringed hair) is a rare hair shaft disorder with alternating light and dark bands along the hair, caused by air filled spaces in the cortex.

It is usually autosomal dominant, with a locus on chromosome 12q24.2 to 12q24.3, and presents in childhood, though cases are sporadic. It affects both sexes and all ethnic groups.

The hair is usually normal in strength and growth, and the condition is benign. It is associated with alopecia areata in some patients.

Pathophysiology.

Clusters of air filled cavities in the hair cortex scatter light, so the affected segments look bright in reflected light and dark in transmitted light. The cause of the cavities is unclear, and an abnormality of the cortical matrix is suspected.

• Shiny, spangled hair with alternating light and dark bands, most visible in fair hair.
• Hair may break at the affected segments in some patients, though most have normal growth.
• Associations: alopecia areata (reported), and rarely other hair shaft disorders.

• Clinical diagnosis from appearance and family history.
• Light microscopy: light bands in transmitted light are dark and in reflected light bright. Dermoscopy and trichoscopy show alternating bands at regular intervals.
• Scanning electron microscopy may show surface irregularity and cavities.

Differential diagnosis.

• Pili torti, trichorrhexis nodosa and monilethrix.
• Banding in trichothiodystrophy (polarised light) and uncombable hair syndrome.
• Hair damage from chemicals and heat.

• Explain the benign nature of the condition. No treatment is needed.
• Gentle hair care: avoid heat, chemical treatments and tight styles.
• Genetic counselling for families (50% risk in dominant disease).

Monitoring. No routine review.

Referral and escalation. Dermatology if hair loss or breakage is troublesome or alopecia areata develops.