Hair Lectures 2024 PDF

Pathophysiology of Hair Disorders Dr A Dadoo MBBCh(Wits), DCH(SA) Photo by Stefan Els Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe...

Pathophysiology of Hair Disorders Dr A Dadoo MBBCh(Wits), DCH(SA) Photo by Stefan Els Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Introduction to hair disorders Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe What is hair? Hair is a complex structure composed of keratinized cells that grow from follicles embedded within the skin Understanding the basic anatomy of hair is essential in comprehending hair growth and various hair-related conditions Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Understanding hair anatomy Source: courses.lumenlearning.com/ Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Understanding hair anatomy Hair is primarily made up of dead, keratinized cells. The hair follicle is the structure within the skin from which the hair shaft emerges The hair shaft is the part of the hair not anchored to the follicle, and much of this is exposed at the skin’s surface (i.e., visible) The rest of the hair, which is anchored in the follicle, lies below the surface of the skin and is referred to as the hair root The hair shaft consists of three main layers: the cuticle, cortex, and medulla Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Understanding hair anatomy The hair bulb surrounds the hair papilla, which is made of connective tissue and contains blood capillaries and nerve endings from the dermis The hair root ends deep in the dermis at the hair bulb and includes a layer of mitotically active basal cells called the hair matrix The hair bulge is a specialized region of the hair follicle located above the hair bulb It serves as a reservoir of stem cells that contribute to the ongoing production of new hair cells during the hair growth cycle and facilitate hair follicle regeneration Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Associated structures Sebaceous glands are associated with hair follicles and secrete sebum, an oily substance that moisturizes and lubricates the hair and the surrounding skin Sebum travels up the hair shaft, helping to maintain its health and flexibility Arrector pili muscle: a small, involuntary muscle attached to the hair follicle When it contracts, it causes the hair to stand upright, resulting in the characteristic phenomenon known as "goosebumps” Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe How does hair grow? Hair grows on most parts of the skin surface, except palms, soles, lips and eyelids Hair thickness and length varies according to the anatomic site Vellus hair is fine, light in colour, and short in length Terminal hair is thicker, darker and longer Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe How does hair grow? A hair shaft grows within a follicle at a rate of about 1 cm per month It 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) Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe The hair growth cycle Hair growth follows a cycle. However, these phases are not synchronised, and any hair may be at a particular phase at random. The main phases of the hair cycle are: Anagen: active growth phase (1-6 years, majority 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 a fourth phase, is the shedding of the hair) Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe The hair growth cycle Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Causes of scarring and non-scarring alopecia Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Scarring and non-scarring alopecia Hair loss (called 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 Understanding the pathophysiology of these causes is crucial for accurate diagnosis and appropriate management of patients presenting with alopecia Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Non-scarring alopecia Hair loss with non-scarring damage to the hair follicles (i.e., the hair loss is usually reversible or treatable). Common causes: Alopecia Areata Telogen Effluvium Male and female pattern hair loss Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Scarring alopecia Hair loss characterized by permanent damage to the hair follicles. Common causes: Discoid Lupus Erythematosus Lichen Planopilaris Chronic bacterial infections Chronic fungal infections Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe The non-scarring alopecias in more detail Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in alopecia areata Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Alopecia areata An autoimmune condition resulting in hair loss It typically presents with discrete bald patches on the scalp, but can cause hair loss from all hair-bearing areas on the body The immune system mistakenly targets the hair follicles as foreign and launches an immune response against them The exact cause of this autoimmune response is not yet fully understood It is hypothesised that loss of immune privilege in anagen hair follicles plays a key role in the pathogenesis Genetic susceptibility is also thought to contribute Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in alopecia areata – autoimmune response The immune system, specifically CD8+ T-lymphocytes, is thought to play a crucial role in the development of alopecia areata These T-lymphocytes infiltrate the hair follicles and recognize specific self-antigens expressed in the hair follicle as foreign or abnormal Thus an immune response is triggered, which leads to inflammation and subsequent damage to the hair follicles Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe 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. This includes numerous human leukocyte antigen (HLA) class I and II alleles, and several alleles of genes involved in immune pathways, hair pigmentation, and response to oxidative stress. The mode of inheritance seems to be complex, and environmental influences are also at play Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in telogen effluvium Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Telogen effluvium In a healthy scalp, about 85% of the hair follicles are actively growing hair (anagen hair) and about 15% are resting hair (telogen hair) A few hairs may also be in catagen A new anagen hair begins to grow under the resting telogen hair and pushes it out A normal or healthy scalp can lose up to about 100 hairs a day on one's comb, brush, in the basin or on the pillow, as a result of the normal scalp hair cycle Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Telogen effluvium Telogen effluvium happens when a significant number of hair follicles prematurely enter the telogen phase (resting phase) of the hair growth cycle, leading to increased hair shedding If there is some insult to the system, as many as 70% of the anagen hairs can be precipitated into telogen, thus reversing the usual ratio This can be triggered by a variety of factors, including physiological, psychological, or environmental stressors Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in telogen effluvium Triggering Factors: Physical or emotional stress (e.g., childbirth, surgery, severe illness, emotional trauma) Hormonal changes (e.g., postpartum hormonal fluctuations, thyroid disorders , discontinuing the contraceptive pill) Nutritional deficiencies (e.g., iron, zinc, biotin) Certain medications (e.g., anticoagulants, retinoids) Rapid weight loss Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in telogen effluvium These triggering factors disrupt the normal balance of the hair growth cycle By causing a large number of hairs in the anagen phase (growing phase of the hair cycle) to abruptly enter the telogen (resting) phase As a result, there is an increased number of hairs in the telogen phase at any given time This then leads to an excess shedding of hair (even with gentle manipulation of the scalp) This increased shedding is noticed by the patient as diffuse hair loss or thinning Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in telogen effluvium Importantly, telogen effluvium is usually a self-limiting condition in the vast majority of people Once the underlying triggering factor is resolved or managed, the affected hair follicles gradually return to their normal growth cycle New hair begins to grow, and the shedding diminishes over time Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of male and female pattern hair loss Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Male and female pattern hair loss Also known as androgenetic alopecia Male pattern hair loss is the most common type of diffuse thinning of the hair and balding that occurs in adult males It is due to a combination of hormones (androgens) and a genetic predisposition It is characterised by a receding hairline and hair loss on the top and front of the head. A similar type of hair loss in women, female pattern hair loss, results in thinning hair on the mid- frontal area of the scalp and is generally less severe than occurs in males Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of male and female pattern hair loss Genetic Predisposition: Androgenetic alopecia is considered a genetically determined condition It is influenced by both maternal and paternal inherited susceptibility genes Several genes have been found to be involved, accounting for differing age of onset, progression, pattern and severity of hair loss in family members Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of male and female pattern hair loss Androgen Sensitivity: The hallmark is the increased sensitivity of hair follicles to androgens, particularly dihydrotestosterone (DHT) DHT is a by-product of testosterone conversion facilitated by the enzyme 5-alpha reductase DHT is believed to shorten the growth, or anagen, phase of the hair cycle, from a usual duration of 3–6 years to just weeks or months This occurs together with miniaturization of the follicles Hair follicles located in certain areas of the scalp, particularly the frontal and vertex regions in men and the central scalp in women, are more susceptible to DHT's effects Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of male and female pattern hair loss Miniaturization of Hair Follicles: The presence of DHT leads to the gradual miniaturization of hair follicles Miniaturization refers to the progressive shrinking of the hair follicles over time The affected hair follicles produce thinner, shorter, and less pigmented hairs during each hair growth cycle, eventually leading to the appearance of thinning or balding areas Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of male and female pattern hair loss A few women present with male pattern hair loss because they have excessive levels of androgens as well as genetic predisposition These women also tend to suffer from acne, irregular menses and excessive facial and body hair These symptoms are characteristic of polycystic ovarian syndrome (PCOS) although the majority of women with PCOS do not experience hair loss Less often, congenital adrenal hyperplasia may be responsible Females that are losing their hair with age are more likely to present with female pattern hair loss, in which hormone tests are normal Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe The scarring alopecias in more detail Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in discoid lupus erythematosus (DLE) Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Discoid Lupus Erythematosus (DLE) Discoid lupus erythematosus (DLE) is a chronic scarring skin condition It is the most common form of cutaneous lupus erythematosus Specifically, it is a sub-type of chronic cutaneous lupus erythematosus It is characterised by persistent scaly plaques on the scalp, face, and ears which subsequently can progress to scarring, atrophy, dyspigmentation, and permanent hair loss in affected hair-bearing areas Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of DLE Lupus erythematosus (LE) is a polygenic autoimmune disease linked to various HLA subtypes, immune signalling, and environmental factors, which ultimately leads to autoantibody production and T-cell dysfunction. However, the exact aetiology of discoid lupus erythematosus (DLE) is not well understood. Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of DLE DLE likely occurs in genetically predisposed individuals, but the exact genetic connection has not been determined. Exogenous factors such as smoking and ultraviolet radiation also play a role: A history of smoking has been found to be more common in those with DLE Ultraviolet radiation can provoke DLE as it is a photosensitive disorder. However, it can be found in non-sun exposed areas as well Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in lichen planopilaris (LPP) Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Lichen planopilaris (LPP) An uncommon inflammatory condition that can lead to permanent hair loss The disease is considered to be a form of lichen planus which affects the hair follicles, and thus having a similar pathogenesis. It results in patchy, progressive, permanent hair loss mainly on the scalp, although other hair- bearing skin (brows, pubic, and body) may be affected. Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of LPP The exact cause of lichen planopilaris is unknown 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, and is also rarely drug-induced. Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in chronic bacterial infections Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in chronic bacterial infections The specific pathophysiology of hair loss in chronic bacterial infections can vary 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. Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in chronic bacterial infections continued Severe bacterial superinfection of chronic scalp conditions (e.g., seborrhoeic eczema) may result in severe inflammation and damage, and eventually permanent destruction of hair follicles Dissecting cellulitis of the scalp is a rare cause of scarring alopecia. This condition is primarily related to follicular hyperkeratosis, rather than infection. However, bacterial superinfection may occur. Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in chronic bacterial infections continued The term folliculitis decalvans is usually applied to forms of highly inflammatory scarring alopecia, where inflammatory, follicular papules and pustules dominate the clinical picture. Often (but not always) Staphylococcus aureus can be grown from pustular or crusted lesions. Some authors believe that a primary staphylococcal infection of the scalp is the cause of folliculitis decalvans. Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in fungal infections Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe Pathophysiology of hair loss in fungal infections Tinea capitis is a common fungal infection of the scalp that most often presents with pruritic, scaling areas of non-scarring hair loss Trichophyton and Microsporum species of dermatophyte fungi are the major causes of tinea capitis The infection is often contracted from another human or an animal through direct contact Tinea capitis does not usually cause a scarring alopecia, unless the infection is long-standing and untreated or severe, or when a clinical variant called a kerion develops Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe 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 the development of an inflammatory plaque with pustules, thick crusting, and/or drainage Kerions appear most commonly in children ages 5 to 10 and are rare in infancy Kerion is most often caused by a zoophilic dermatophyte; however, anthropophilic fungi can also cause a kerion Persistent kerion can lead to scarring alopecia Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe  Thank you Enkosi Dankie Photo by Stefan Els Medicine and Health Sciences · EyeNzululwazi ngezoNyango neMpilo · Geneeskunde en Gesondheidswetenskappe