Hair restoration classification of hair



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Lip Teh

December 05



HAIR RESTORATION
Classification of hair

Morphological



  1. Lanugo – fetal hair

  2. Vellus hair – fine, hypopigmented hair in truncal/extremities

  3. Terminal hair – scalp, face, groin, axilla




  • Same hair follicles can produce both terminal and vellus hair at different phases of life.


Embryology

  • third month of gestation, the epithelial primary hair germs develop in the eyebrow region and scalp.

  • Subsequently, hair development continues in a cephalocaudal direction.

  • The primary hair germ begins as an epithelial bud that protrudes into the dermis -directed by a collection of mesenchymal cells that eventually form the dermal (follicular) papilla.

  • Acquires multiple epithelial buds that grow transversely and differentiate into the many components of the primary hair follicle (ie, sebaceous gland and duct, apocrine gland and duct, attachment point of the erector pili muscle [bulge region]).

  • Average scalp has 100,000 hair follicles


Structure

  • Pilosebaceous Unit (Pilosebaceous Follicle)

  1. Hair follicle

  2. Sebaceous Gland

  3. Arrector Pili Muscle

  • Hair follicle components:

  1. Bulb consists of the Dermal papilla and the hair matrix

  2. Dermal papilla

    1. contains androgen receptors, capillaries

  3. Melanocytes

    1. present upper part of papilla

    2. array of hair colors observed is derived from varying ratios of brown/black eumelanins and yellow/red pheomelanins

    3. binding of alpha-melanocyte-stimulating hormone (MSH) to melanocortin 1 receptor lead to a production switch from pheomelanin to eumelanin

    4. White hairs due to eventual fatigue of the follicular melanocyte reservoir’s ability to repopulate the new hair matrix

  4. Hair matrix

    1. surrounds the top and sides of the dermal papilla

    2. Actively growing portion of the follicle consisting of epidermal stem cells that rapidly divide(24-72 hours) , move upward, and give rise to the hair shaft and the internal root sheath

  5. Hair shaft

    • composed primarily of keratin

    • visible hair shaft is the dead protein end-product hair matrix that is deep in the subcutaneous fat at the base of the hair follicle canal.

    • Haor culr determined by cross sectional shape. Circular = straight, Elliptical = Curly

    • A shaft of hair has three keratinised layers:

  1. Medulla

  2. Cortex

    • middle layer, thickest

    • provides strength, color, texture, and elasticity (curly vs straight)

  3. Cuticle

    • colorless and forms a tightly-packed protective layer of overlapping scales

  1. Root sheath

    1. Internal Root Sheath (lightly keratinized)

      1. closely apposed to the hair shaft

      2. coats and supports the hair shaft up to the level of the isthmus (sebaceous gland)

    2. Outer Root Sheath

      1. Covers the IRS, continuous with epithelium

  2. Arrector Pili Muscle

    1. Smooth muscle attached to hair follicle (bulge area)

    2. Contraction erects hair

    3. Innervated by sympathetic nervous system

    4. Activated by fear or cold




Phases of cyclic hair growth


  • Anagen: Growing phase (85-90% of hair cycle)

    • Eyebrow and eyelash growth phase lasts 1 to 6 months

    • Scalp hair growth phase lasts 2 to 6 years

    • Scalp hair grows 0.4 mm/day or 10cm per year

  • Catagen: Transition or rapid involution phase (2-3%)

    • 2-3 weeks

    • hair follicle shrinks to about 1/6 of its normal length.

    • lower part of the follicle is destroyed and the dermal papilla breaks away with a part of root sheath = secondary germ unit

    • hair bulb becomes keratinized (club hair) and is pushed upward to the surface by a column of epithelial cells.

  • Telogen: Resting phase (10-15% of hair cycle)

    • Mustache hair resting phase lasts 1.5 months

    • Scalp resting phase lasts 3 to 6 months

    • As telogen ends, hair ejected and anagen starts again

    • 100 scalp hair loss per day

    • Telogen hairs show have short, club-shaped roots lacking root sheaths and show depigmentation of the proximal parts of the shaft.

  • Unlike animals, human hair have a mosaic growth pattern.


Causes of Hair Loss
Scarring

    1. Traction alopecia

    1. Trauma – burns

    2. Infections

    3. Autoimmune – SLE, scleroderma

    4. Iatrogenic – laser, poor surgical technique (bevel incisions)

    5. Congenital – cutis aplasia


Nonscarring

  1. Physiological

    • Male pattern baldness (androgenetic alopecia)

    • Female pattern baldness

      1. Unlike males, usually nonuniform diffuse hair loss

      2. often preserves the anterior hairline

      3. Warrants endocrinology assessment

  2. Telogen Effluvium

    • Early and excessive loss of normal club hairs from normal resting follicles

    • occurs within1-6months following stresses and other triggering factor

    • gentle pull test (normal <5 hairs, abnormal 10-20 mainly club hairs)

    • punch biopsy shows lower anagen:telogen ratio; normal hair follicles

    • Causes

  1. Pyrexia, sepsis

  2. Childbirth (rarely)

  3. Major surgery

  4. Protein deficiency due to unsupervised crash diets.

  5. Drugs including beta blockers, retinoids, antidepressants.

  6. Severe psychological stress

  1. Anagen Effluvium

  • significant loss of hairshafts in their Anagen phase.

  • Rapid onset (e.g. within 2-4 weeks of the cause).

  • Punch biopsy shows normal anagen-to-telogen ratio with normal

  • Hair regrows spontaneously.

  • Hair that grows back may show a change in the texture and color.

  • Causes - any insult to the hair follicle that impairs its mitotic or metabolic activity:

  1. Chemotherapy drugs (worse with doxorubicin, the nitrosoureas, and cyclophosphamide.) – dose dependant

    1. Apparent 1-2 weeks after treatment and worst 1-2 months

  2. Radiotherapy – dose dependant

  3. Malnutrition

  4. Oral contraceptives

  5. Vitamin A poisoning

  6. Iron deficiency

  7. Chronic infections – syphilis



  1. Alopecia Areata

    • Autoantibodies directed to anagen phase follicles

    • peribulbar lymphocytic infiltrate on biopsy (swarm of bees)

    • increased vellus hairs




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