Introduction to Hair Disorders

Introduction to Hair Disorders

• Hair is a complex structure composed of keratinized cells that grow from follicles embedded within the skin.

Understanding Hair Anatomy

• Hair is primarily composed of dead, keratinized cells.
• A hair shaft grows within a follicle at a rate of about 1 cm per month.
• This growth is due to cell division within the hair bulb at the base of the follicle.
• The cells produce the three layers of the hair shaft (medulla, cortex, cuticle).
• The hair shaft is mainly composed of the protein keratin (which is also a major component of skin and nails).

The Hair Growth Cycle

• Hair growth follows a cycle with three main phases:
  • Anagen: active growth phase (1-6 years, majority of hairs are in this phase)
  • Catagen: transitional phase of 1-3 weeks when growth stops, and the follicle shrinks (1–3% of hairs)
  • Telogen: resting phase for 1-4 months (up to 10% of hairs in a normal scalp)
  • Exogen: shedding of the hair

Causes of Scarring and Non-Scarring Alopecia

• Hair loss (alopecia) can be an isolated problem or associated with another disease or condition.
• It can be non-scarring (temporary or reversible) or scarring (permanent), depending on the cause.

Non-Scarring Alopecia

• Hair loss with non-scarring damage to the hair follicles (hair loss is usually reversible or treatable).
• Common causes:
  • Alopecia Areata
  • Telogen Effluvium
  • Male and female pattern hair loss

Scarring Alopecia

• Hair loss characterized by permanent damage to the hair follicles.
• Common causes:
  • Discoid Lupus Erythematosus (DLE)
  • Lichen Planopilaris (LPP)
  • Chronic bacterial infections
  • Chronic fungal infections

The Non-Scarring Alopecias in More detail

• Non-scarring alopecia is hair loss with non-scarring damage to the hair follicles.

Pathophysiology of Hair Loss in Alopecia Areata

• Alopecia Areata is an autoimmune condition resulting in hair loss, typically presenting with discrete bald patches on the scalp.
• The immune system mistakenly targets hair follicles as foreign and launches an immune response against them.
• The exact cause of this autoimmune response is not yet fully understood.
• Loss of immune privilege in anagen hair follicles is thought to play a key role.
• Genetic susceptibility is also thought to contribute.

Pathophysiology of Hair Loss in Alopecia Areata – Autoimmune Response

• CD8+ T-lymphocytes are thought to play a crucial role in alopecia areata development.
• These lymphocytes infiltrate hair follicles and recognize specific self-antigens as foreign or abnormal.
• This triggers an immune response, leading to inflammation and hair follicle damage.

Pathophysiology of Hair Loss in Alopecia Areata – Genetic and Other Factors

• Alopecia areata has a strong hereditary component. At least 16 genetic risk loci have been detected.

Pathophysiology of Discoid Lupus Erythematosus (DLE)

• DLE likely occurs in genetically predisposed individuals.
• Exogenous factors like smoking and ultraviolet radiation also play a role (DLE is a photosensitive disorder).

Pathophysiology of Hair Loss in Lichen Planopilaris (LPP)

• Lichen planopilaris is an uncommon inflammatory condition that can lead to permanent hair loss.
• It is considered a form of lichen planus affecting the hair follicles.
• It results in patchy, progressive, permanent hair loss mainly on the scalp.
• The exact cause is unknown, but it is thought to be a cytotoxic autoimmune response to an unknown antigen located in hair follicles.
• The exact trigger for this immune response is not fully understood.
• The disease may rarely be gene-related or drug-induced.

Pathophysiology of Hair Loss in Chronic Bacterial Infections

• The specific pathophysiology of hair loss in chronic bacterial infections varies depending on:
  • The type of bacteria involved (e.g., staphylococcus aureus).
  • The location and severity of the infection (e.g., scalp).
  • Individual patient factors (e.g., underlying HIV).
• Bacterial scalp infections presenting as scalp folliculitis do not usually result in scarring hair loss.

Pathophysiology of Hair Loss in Chronic Bacterial Infections Continued

• Severe bacterial superinfection of chronic scalp conditions (e.g., seborrhoeic eczema) may result in permanent hair follicle destruction.
• Dissecting cellulitis of the scalp is a rare cause of scarring alopecia.

Pathophysiology of Hair Loss in Chronic Bacterial Infections Continued

• Folliculitis decalvans is a highly inflammatory scarring alopecia often associated with Staphylococcus aureus.

Pathophysiology of Hair Loss in Fungal Infections

• Tinea capitis is a common fungal infection of the scalp presenting with pruritic, scaling areas of non-scarring hair loss.
• Trichophyton and Microsporum species of dermatophyte fungi are the major causes.
• The infection is often contracted from another human or an animal through direct contact.
• Tinea capitis does not usually cause scarring alopecia unless the infection is long-standing, untreated, or severe.

Pathophysiology of Hair Loss in Fungal Infections - Kerion

• Kerion is a severe manifestation of tinea capitis resulting from a dramatic immune response to the infection.
• It is characterized by an inflammatory plaque with pustules, thick crusting, and/or drainage.
• Persistent kerion can lead to scarring alopecia.

This quiz explores the complexities of hair structure and anatomy, detailing the composition and growth cycle of human hair. Participants will learn about keratin's role, the phases of the hair growth cycle, and the characteristics of each phase. Ideal for those interested in dermatology or trichology.