Trichorrhexis Invaginata

Trichorrhexis invaginata (bamboo hair) is a structural hair shaft defect in which the distal part of the hair shaft telescopes into the proximal part, forming a ball-and-socket joint that breaks easily.

It is the characteristic hair finding of Netherton syndrome (SPINK5 variants, autosomal recessive), and is seen in almost all affected patients, though it may be absent in infancy. It is rarely reported in other disorders, and the hair may appear normal in some patients.

It affects scalp hair, eyebrows and eyelashes. Hair is short, sparse and brittle.

Pathophysiology.

Premature or abnormal cornification of the hair cortex, from loss of the protease inhibitor LEKTI, leaves a soft zone in the shaft that is pushed into by the harder distal portion, giving the invagination.

• Short, dull, sparse and fragile hair, with broken shafts, and sparse eyebrows (often the first site).
• Features of Netherton syndrome: congenital ichthyosiform erythroderma or ichthyosis linearis circumflexa, atopic features and raised IgE.
• Hair can improve with age.

• Light microscopy of plucked eyebrow and scalp hairs: nodes with a cup (socket) and ball, giving a bamboo or golf tee appearance. Several hairs from different sites should be examined.
• For suspected Netherton syndrome: LEKTI immunostaining of the skin, IgE and SPINK5 sequencing.

Differential diagnosis.

• Trichorrhexis nodosa, pili torti and monilethrix.
• Pili annulati, trichothiodystrophy and loose anagen hair.
• Acquired fragility from chemicals, heat or trauma.

• Treat the cause: Netherton syndrome needs emollients, careful infection control, nutritional support and monitoring of allergy.
• Gentle hair care: soft brushing, no heat, no tight styles and no chemical treatments. Hair conditioners help the appearance.
• Reassure the family that hair often thickens with age.
• Genetic counselling for families with Netherton syndrome (25% recurrence risk).

Monitoring. Review with the dermatology team of the underlying condition.

Referral and escalation. Paediatric dermatology and genetics.