Hair Shaft Abnormalities

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Hair Shaft Intro - Hairy Foundations

Hair shaft structure diagram

  • Structure: Hair shaft comprises three layers:
    • Cuticle: Outermost, protective, overlapping scales.
    • Cortex: Main bulk, contains melanin (pigment) and keratin.
    • Medulla: Innermost core, may be absent in fine hair.
  • Abnormalities Classification:
    • Fractures (e.g., Trichorrhexis nodosa)
    • Irregularities/Invaginations (e.g., Pili annulati)
    • Coiling/Twisting (e.g., Pili torti)
    • Extraneous Matter (e.g., Piedra)

⭐ The cuticle is the first layer damaged by external factors like heat and chemicals, leading to dull, brittle hair.

Genetic Fragility - Brittle Breakdowns

Key genetic conditions causing hair fragility and breakage:

DisorderMicroscopic Appearance & InheritanceClinical Features & Associations
MonilethrixElliptical nodes & constrictions ("beaded hair"); AD (KRT genes)Sparse, fragile, short hair; follicular hyperkeratosis. Improves with age.
Trichorrhexis NodosaNode-like swellings, brush-like fractures ("two brooms"); Genetic/AcquiredBrittle hair, easy breakage; Argininosuccinic aciduria, Menkes.
Pili TortiFlattened shaft, twisted 180° on its axis; AD/ARBrittle, coarse, spangled/glistening hair; alopecia. Menkes, Bjornstad.
Trichorrhexis Invaginata"Bamboo hair" (ball-and-socket invagination); AR (SPINK5)Short, sparse, fragile hair. Pathognomonic for Netherton Syndrome.

⭐ Trichorrhexis invaginata ("bamboo hair") is pathognomonic for Netherton syndrome.

Genetic Morphology - Curious Coils & Coifs

  • Inherited hair shaft structural variants; unique textures, not primarily fragile.
AbnormalityInheritanceFeaturesMicroscopic (Shaft)Associations
Pili AnnulatiADLight/dark bands ("ringed"), normal strengthMicroscopy of Pili Annulati Bright (air) & dark bandsIsolated
Uncombable Hair SyndromeAD/ARSilvery, frizzy, unmanageable; improves with ageUncombable Hair Syndrome: Clinical and Microscopic View Triangular/grooved cross-sectionIsolated
Woolly HairAD/ARTightly coiled, fine, hypopigmented; diffuse/localElliptical cross-section, ↓diameterNaxos/Carvajal (cardiac)
Pili TortiAD/AR/XLRFlattened, twisted 180°; brittle, glisteningTwists of flattened shaftMenkes, Björnstad, Crandall

Acquired Damage - Environmental Endings

  • Trichoptilosis (Split Ends): Longitudinal splitting of distal hair shaft.
    • Causes: Excessive grooming, weathering, chemical treatments.
    • Mgt: Trim ends, gentle care. Microscopic view of trichoptilosis (split ends)
  • Trichoclasis: Transverse "greenstick" fracture of shaft.
    • Cause: Trauma (e.g., vigorous brushing).
  • Trichorrhexis Nodosa: Most common defect; nodes where cuticle is lost, fibers fray (like two brooms).
    • Causes: Physical (brushing, heat) or chemical trauma.

    ⭐ Acquired trichorrhexis nodosa is the most common cause of brittle hair.

  • Bubble Hair: Air-filled cavities (bubbles) in shaft.
    • Cause: Acute localized overheating (e.g., faulty hair dryer). Hair becomes brittle.
    • Microscopy: "Swiss cheese" appearance. Hair Shaft Abnormalitiesoka

Clinical Approach - Scalp Scope & Strategy

  • History: Onset, progression, family history, hair care practices, chemical exposures.
  • Examination:
    • Scalp: Scaling, inflammation, alopecia pattern.
    • Hair pull test: Assesses active shedding (normal < 6-10 hairs).
    • Wood's lamp: Fungal infections (e.g., Microsporum fluoresces).
  • Trichoscopy: Non-invasive; visualizes hair shafts, follicles, perifollicular skin.

    ⭐ Trichoscopy significantly aids in differentiating various hair shaft disorders by revealing specific morphological features (e.g., nodes, constrictions, fractures).

  • Hair Mount Microscopy: Plucked/cut hairs examined under light microscope; KOH mount for fungi.

Microscopy of hair shaft abnormalities

High‑Yield Points - ⚡ Biggest Takeaways

  • Monilethrix: Beaded hair (AD, Keratin genes), leads to patchy alopecia.
  • Pili torti: Twisted hair, associated with Menkes syndrome (copper deficiency).
  • Trichorrhexis nodosa: Most common defect; "two brooms" appearance; acquired or congenital.
  • Trichorrhexis invaginata (Bamboo hair): Pathognomonic for Netherton syndrome (SPINK5).
  • Pili annulati: Ringed hair (alternating light/dark bands); hair glistens.
  • Uncombable hair syndrome: Spun glass hair (triangular on cross-section); PADI3, TGM3, TCHH genes.
  • Trichothiodystrophy: Sulfur-deficient brittle hair ("tiger tail" banding); associated with PIBIDS.

Practice Questions: Hair Shaft Abnormalities

Test your understanding with these related questions

A 10-year-old boy presented with painful boggy swelling of scalp, multiple sinuses with purulent discharge, easily pluckable hair, and lymph nodes enlarged in occipital region, which of the following would be most helpful for diagnostic evaluation?

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Flashcards: Hair Shaft Abnormalities

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During _____ phase of hair cycle, the proximal end of the hair shaft keratinizes to form a club-shaped structure and the lower part of the follicle involutes by apoptosis.

TAP TO REVEAL ANSWER

During _____ phase of hair cycle, the proximal end of the hair shaft keratinizes to form a club-shaped structure and the lower part of the follicle involutes by apoptosis.

catagen

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