Alopecia

Alopecia is the loss of hair in areas anywhere on the body where hair normally grows. Alopecia may be defined as scarring or non-scarring, localized or diffuse, congenital or acquired, reversible or permanent, or confined to the scalp or universal; however, alopecia is usually classified using the 1st 3 factors. The etiologies of alopecia are usually divided into disorders in which the hair follicle is abnormal or damaged and those in which the hair follicle is normal but the cycling of hair growth is abnormal. The most common presentations are androgenetic hair loss, alopecia areata, traction alopecia, tinea capitis, and telogen effluvium. Diagnosis is made through a positive medical history and physical exam findings. Treatment depends on the type and potential for regrowth.

Last update:

February 1, 2021
8:38 am

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Overview

Normal phases of hair growth

Anagen:
- Period of active growth
- Approximately 90% of all hair follicles are in the anagen phase.
- Lasts 2–6 years
Catagen:
- Transitory period of follicular degeneration or regression
- < 1% of all hair follicles are in the catagen phase.
- Lasts 2–3 weeks
Telogen:
- Period of rest
- Approximately 10% of all hair follicles are in the telogen phase.
- Lasts 2–3 months
After the telogen phase, hairs fall out at a rate of 50–100 scalp hairs per day.

Stages of hair growth — The 3 stages of hair growth:
Anagen represents the periods of active growth; 90% of all hair follicles are in the anagen phase. Catagen represents the periods of degeneration and regression of the hair follicle; < 1% of all hair follicles are in the catagen phase. Telogen represents the resting periods; < 10% of all hair follicles are in the telogen phase. After the telogen phase, the hair naturally falls out.
Image by Lecturio.

Classification or types of alopecia

The most common classifications of hair loss are cicatricial (scarring) alopecia, non-scarring alopecia, and structural hair disorders.

Cicatricial (scarring):

The hair follicle undergoes irreversible damage, which heals through fibrosis, leading to a cessation in hair cycling and permanent hair loss.

Secondary: caused by inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation due to physical trauma or a condition that is not a primary scalp disease (includes tinea capitis, neoplasms, radiation therapy, and surgical scars)
Primary: caused by inflammatory disorders of the scalp in which the hair follicle is the main target in destruction, resulting in permanent hair loss (divided into 3 subtypes: lymphocytic, neutrophilic, and mixed)

**Table: Subtypes of primary cicatricial alopecia**
Lymphocytic	Neutrophilic	Mixed
Alopecia mucinosa Central centrifugal cicatricial alopecia Discoid lupus erythematosus Keratosis follicularis spinulosa decalvans Lichen planopilaris Frontal fibrosing alopecia	Dissecting cellulitis Cellulitis Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. Cellulitis of the scalp Folliculitis decalvans	Acne keloidalis nuchae Acne necrotica Erosive pustular dermatosis of the scalp

Non-scarring:

Inflammation is mild or absent so that the hair follicle is not damaged, resulting in non-permanent hair loss (divided into 3 subtypes: focal, patterned, and diffuse).

**Table: Subtypes of non-scarring alopecia**
Focal	Patterned	Diffuse
Alopecia areata Alopecia syphilitica Pressure-induced (postoperative) alopecia Temporal triangular alopecia Traction alopecia	Androgenetic alopecia in men (male-pattern hair loss) Female-pattern hair loss Trichotillomania Trichotillomania Trichotillomania (hair-pulling disorder (HPD)) is defined as repetitive pulling of one's hair resulting in hair loss that may be visible to others. This disorder is classified under obsessive-compulsive and related disorders, as there is tension prior to the act that is relieved after the hair-pulling. Trichotillomania	Anagen effluvium Loose anagen syndrome Telogen effluvium

Structural hair disorders:

Structural hair disorders are inherited or acquired disorders of hair structure that result in brittle or fragile hair, which lead to hair breakage or the appearance of hair growth failure.

**Table: Structural hair disorders**
Inherited	Acquired
Menkes disease Monilethrix Trichothiodystrophy Trichorrhexis invaginata	Trichorrhexis nodosa Trichoptilosis

Diagnosis

Medical history:

It’s important to determine the duration, rate of progression, location, pattern, and extent of hair loss along with the patient’s associated symptoms, medical disorders/events, family history of hair loss, medications, and diet/caloric intake.
Drugs associated with hair loss:
- Amantadine
- Amiodarone
- Isotretinoin
- Anticoagulants Anticoagulants Anticoagulants are drugs that retard or interrupt the coagulation cascade. The primary classes of available anticoagulants include heparins, vitamin K-dependent antagonists (e.g., warfarin), direct thrombin inhibitors, and factor Xa inhibitors. Anticoagulants
- Ketoconazole
- Anticonvulsants
- Lithium
- Captopril
- Penicillamine
- Statins Statins Statins are competitive inhibitors of HMG-CoA reductase in the liver. HMG-CoA reductase is the rate-limiting step in cholesterol synthesis. Inhibition results in lowered intrahepatocytic cholesterol formation, resulting in up-regulation of LDL receptors and, ultimately, lowering levels of serum LDL and triglycerides. Statins
- Propranolol
- Cimetidine
- Colchicine
Medical conditions associated with hair loss:
- Major illness, surgery, and/or psychologic stress
- Significant weight loss
- Chronic iron deficiency
- Thyroid disorders
- Childbirth
- Poisoning from arsenic, mercury, or thallium

Physical exam:

Visual inspection:
- Presence versus absence of follicular ostia (absence = scarring alopecia)
- Distribution and density of hair
- Pattern of hair loss
- Use of contrasting colored paper to fully visualize hair
- Examine other sites of hair plus nails, skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, and teeth Teeth Normally, an adult has 32 teeth: 16 maxillary and 16 mandibular. These teeth are divided into 4 quadrants with 8 teeth each. Each quadrant consists of 2 incisors (dentes incisivi), 1 canine (dens caninus), 2 premolars (dentes premolares), and 3 molars (dentes molares). Teeth are composed of enamel, dentin, and dental cement. Teeth
Trichoscopy: dermoscopy of the hair and scalp, which allows for better visualization of the epidermis, follicular ostia, hair shafts, scale, erythema, and blood vessels
Hair pull test: identifies active hair loss by grasping and slightly tugging 50–60 hair fibers, easy extraction of > 6 hair fibers suggests active hair loss

Normal scalp trichoscopy:
Multiple hair fibers can be seen to emerge from a single infundibulum.
Image: “Figure 4” by Rodney Sinclair et al. License: CC BY 4.0

Scalp with androgenic alopecia — Normal scalp trichoscopy:
Multiple hair fibers can be seen to emerge from a single infundibulum.
Image: “Figure 4” by Rodney Sinclair et al. License: CC BY 4.0

Additional tests:

Microscopy: microscopic evaluation of the proximal hair ends, which is useful for determining the phase of the shedding hair
Scalp biopsy: used in scarring forms of alopecia to distinguish inflammatory from non-inflammatory causes
Trichograms and phototrichograms: used to evaluate non-scarring hair loss and treatment response
Laboratory:
- Thyroid-stimulating hormone (TSH) to assess thyroid disorders
- Serum iron and ferritin to assess iron deficiency
- Rapid plasma reagin test to assess for syphilis Syphilis Syphilis is a bacterial infection caused by the spirochete Treponema pallidum pallidum (T. p. pallidum), which is usually spread through sexual contact. Syphilis has 4 clinical stages: primary, secondary, latent, and tertiary. Syphilis

Androgenetic Alopecia

Definition

Androgenetic alopecia is a hereditary type of hair loss that is mediated by the presence of the androgen dihydrotestosterone (DHT) and is the most common type of alopecia.

Male-pattern hair loss

Epidemiology:
- Most common alopecia in men
- Prevalence increases with age.
- Affects 80% of men by age 80
- Lower prevalence in Chinese, Asian, and African Americans than in Caucasians
Etiology:
- Genetic predisposition (androgen-dependent trait)
- Related to the X chromosome
Pathophysiology:
1. Testosterone is converted to DHT by 5-alpha-reductase.
2. DHT binds to the androgen receptor in hair follicles and activates genes that shorten the anagen phase.
3. Leads to follicular miniaturization of hair follicles of the scalp (a progressive decrease in the ratio of terminal hairs to shorter, thinner vellus hairs)
Clinical presentation:
- Hair loss can begin any time after puberty Puberty Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11-19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Puberty (usually in the late 20s) and progresses over the patient’s lifetime.
- Receding mid-temporal hairline
- Vertex has diffuse thinning/balding with intact frontal hair.
- Preservation of hair density in the occipital region
- Visible reduction in hair density
Diagnosis: based on history and exam
Management:
- 1st-line therapy:
  - Oral finasteride: 5-alpha-reductase inhibitor that inhibits the conversion of testosterone to DHT and inhibits follicular miniaturization
  - Topical minoxidil: vasodilator that increases the duration of anagen, shortening telogen, and enlarging miniaturized follicles
- Other options:
  - Hair transplant surgery
  - Low-level laser light therapy
  - Cosmetic use of hairpieces

Female-pattern hair loss

Epidemiology:
- A common condition affecting 19% of Caucasian women
- Most commonly occurs following menopause Menopause Menopause is a physiologic process in women characterized by the permanent cessation of menstruation that occurs after the loss of ovarian activity. Menopause can only be diagnosed retrospectively, after 12 months without menstrual bleeding. Menopause
- Prevalence increases with age, with ⅓ of women being affected by age 70.
Etiology:
- Not well understood
- Androgen excess may play a role.
- Genetic predisposition is suspected.
Pathophysiology:
- Transformation of the terminal hair follicle to a thinner vellus hair follicle via follicular miniaturization
- Shortened anagen phase and lengthened telogen phase
Clinical presentation:
- Diffuse thinning of hair
- Frontal hairline is thinned yet preserved.
- Progressively widening midline part leading to crown thinning
- Preservation of hair density in the occipital region
Diagnosis:
- Based on history and exam
- Laboratory: Free and total testosterone level and dehydroepiandrosterone sulfate (DHEAS) level can test for an underlying hyperandrogenic state.
Management:
- 1st-line therapy: topical minoxidil (vasodilator that increases the duration of anagen, shortening telogen, and enlarging miniaturized follicles)
- 2nd-line therapies:
  - Spironolactone: aldosterone antagonist that competitively blocks androgen receptors and inhibits androgen synthesis
  - Finasteride: 5-alpha-reductase inhibitor that inhibits the conversion of testosterone to DHT and inhibits follicular miniaturization
- Other options:
  - The use of wigs or cosmetic camouflaging
  - Hair transplant surgery

Alopecia Areata

Definition

Alopecia areata is a chronic, relapsing, autoimmune disorder in which the body’s immune system targets anagen hair follicles and causes non-scarring hair loss.

Epidemiology

Occurs in 1% of the population
The lifetime risk is approximately 2%.
Occurs at similar rates in males and females
The average age of onset is approximately 30 years.

Etiology

Autoimmune disease, where hair follicles are targeted and transition prematurely from the anagen growth phase to the catagen and telogen phases
Genetic predisposition also plays a role.
Associated disorders:
- Other autoimmune diseases: vitiligo Vitiligo Vitiligo is the most common depigmenting disorder and is caused by the destruction of melanocytes. Patients present with hypo- or depigmented macules or patches which often occur on the face, hands, knees, and/or genitalia. Vitiligo, lupus, psoriasis Psoriasis Psoriasis is a common T-cell-mediated inflammatory skin condition. The etiology is unknown, but is thought to be due to genetic inheritance and environmental triggers. There are 4 major subtypes, with the most common form being chronic plaque psoriasis. Psoriasis, scleroderma Scleroderma Scleroderma (systemic sclerosis) is an autoimmune condition characterized by diffuse collagen deposition and fibrosis. The clinical presentation varies from limited skin involvement to diffuse involvement of internal organs. Scleroderma, thyroiditis Thyroiditis Thyroiditis is a catchall term used to describe a variety of conditions that have inflammation of the thyroid gland in common. It includes pathologies that cause an acute illness with severe thyroid pain (e.g., subacute thyroiditis and infectious thyroiditis) as well as conditions in which there is no clinically evident inflammation and the manifestations primarily reflect thyroid dysfunction or a goiter (e.g., painless thyroiditis and fibrous Riedel's thyroiditis). Thyroiditis, celiac disease Celiac disease Celiac disease (also known as celiac sprue or gluten enteropathy) is an autoimmune reaction to gliadin, which is a component of gluten. Celiac disease is closely associated with HLA-DQ2 and HLA-DQ8. The immune response is localized to the proximal small intestine and causes the characteristic histologic findings of villous atrophy, crypt hyperplasia, and intraepithelial lymphocytosis. Celiac Disease, atopic dermatitis Atopic Dermatitis Atopic dermatitis, also known as eczema, is a chronic, relapsing, pruritic, inflammatory skin disease that occurs more frequently in children, although adults can also be affected. The condition is often associated with elevated serum levels of IgE and a personal or family history of atopy. Skin dryness, erythema, oozing, crusting, and lichenification are present. Atopic Dermatitis (Eczema), allergic rhinitis Rhinitis Rhinitis refers to inflammation of the nasal mucosa. The condition is classified into allergic, nonallergic, and infectious rhinitis. Allergic rhinitis is due to a type I hypersensitivity reaction. Non-allergic rhinitis is due to increased blood flow to the nasal mucosa. Infectious rhinitis is caused by an upper respiratory tract infection. Rhinitis
- Genetic disorders: Down’s syndrome
- Psychosocial disorders: stress, anxiety, mood disorders