Alopecia

Alopecia is the loss of hair from any hair-bearing area of the body, but most often the scalp. It may be congenital or acquired, circumscribed or diffuse, and cicatricial or nonscarring. Androgenetic alopecia, a type of diffuse, nonscarring, acquired alopecia, is the most common, affecting > 70% of the general population by 70 years of age. Alopecia areata, an acquired, circumscribed, nonscarring alopecia, is the next most common type. Clinical diagnosis is usually possible. In ambiguous cases, diagnosis is aided by microscopic examination of the hair, trichograms, and scalp biopsy. Treatment depends on the type of alopecia and includes long-term (at least 1 year) use of topical minoxidil, corticosteroids (topical, intralesional, or oral), or antiandrogens. Surgery (hair transplant) or camouflaging techniques are used when medical therapy fails. The prognosis is variable and depends on the etiology and severity of hair loss.

Definitions

• Alopecia: : loss of hair (baldness)
• Effluvium : process of hair loss
• Atrichia : inherited hair loss
• Hypotrichosis : congenital sparse hair, which is usually associated with syndromes such as:
  • Netherton syndrome: autosomal recessive disorder caused by mutations in SPINK5, a gene that encodes a serine protease kinase.
  • Rothmund-Thomson syndrome: syndrome characterized by short stature, sparse hair, poikiloderma, skeletal abnormalities, and cataracts.

Phases of hair growth

• Anagen phase: phase of active growth
• Telogen phase: resting phase
• Catagen phase: phase of follicular regression

Classification

According to etiology (congenital/acquired) and pattern (diffuse/circumscribed)

According to the presence of scarring

• Cicatricial (scarring) alopecia
  • Brocq pseudopelade
    • Seen in women 30–55 years of age
    • Irregular areas of irreversible hair loss, which become scarred areas at a later stage
  • Lichen planopilaris
  • Frontal fibrosing alopecia (a progressive form of frontotemporal hair loss associated with local scarring)
  • Central centrifugal cicatricial alopecia
    • Alopecia that starts at the crown and spreads outwards
    • Occurs almost exclusively in black women > 50 years
  • Skin conditions causing scarring alopecia; : ichthyosis, dyskeratosis, discoid lupus erythematosus
  • Acquired scarring alopecia (e.g., via viral diseases, mycoses, burns, chemical burns)
• Nonscarring alopecia
  • Alopecia areata
  • Telogen effluvium
  • Traction alopecia
  • Temporal triangular alopecia

Diagnosis

The diagnosis is often clear from the patient history and physical examination; however, there are several tests that allow confirmation of diagnosis.

• Hair pull test: About 50 strands of hair are lightly tugged away from the scalp; if > 5 strands can be pulled out, the test is positive.
• Dermoscopy: examination of the scalp skin, follicle size, and hair shaft diameter by magnification
• Microscopic examination: performed on hair follicles and shaft to determine the phase of hair growth (anagen, telogen) and structural abnormalities of the shaft
• Scalp biopsies (performed from sites of active disease): to confirm the diagnosis of cicatricial alopecia
• Trichograms: aids diagnosis and prognosis of nonscarring alopecia

References:^{[1][2][3][4][5][6][7]}

Congenital diffuse alopecia

• Trichorrhexis nodosa: A hair shaft deformity characterized by the development of weak points in the shaft due to physical/chemical trauma in genetically predisposed individuals.
• Pili torti: The hair shaft is flattened and has multiple twists which lead to fragile hair that breaks easily.
• Monilethrix (beaded hair): Autosomal dominant disorder with beaded hair shafts which break easily, close to the scalp, a few months after birth.
• Genetic syndromes: Menkes disease, Netherton's syndrome, etc.

Acquired diffuse alopecia

Androgenetic alopecia

• Definition: a progressive, nonscarring alopecia that affects the regions of the scalp with the most androgen-sensitive hair follicles, resulting in a characteristic pattern of balding (bitemporal scalp in men and vertex and frontal scalp in women).
• Epidemiology
  • Most common type of alopecia
  • Prevalence: Increases with age
  • Sex: ♂ > ♀ (but very common in women as well)
  • Age at onset: puberty in males; menopause in females
  • Ethnicity: more common in white populations
• Etiology
  • Increased androgen sensitivity of hair follicle in genetically predisposed individuals
  • Uncommon causes
    • Congenital adrenal hyperplasia
    • Androgen-producing tumors: Leydig cell tumor, arrhenoblastoma
• Pathophysiology
  • Follicular miniaturization: Androgen shortens the anagen phase of hair growth → vellus hair formation (thin, short hair)
  • The 5α-reductase enzyme present in hair follicles converts testosterone into the more potent dihydrotestosterone, which is responsible for alopecia.
• Differential diagnosis
  • Diffuse alopecia areata
  • Telogen effluvium

Telogen effluvium

• Etiology
  • Endocrine: hypothyroidism, hypopituitarism, hypoparathyroidism, hyperthyroidism, diabetes mellitus ^[8]
  • Drugs: anabolic steroids, antithyroid drugs, heparin, coumarin, antimetabolites (chemotherapy), oral contraceptives, etc.
  • Nutritional: hypervitaminosis A, zinc deficiency, malnutrition states
  • Stress: major surgery, sepsis, after childbirth (telogen gravidarum), acute or chronic illness (e.g., systemic lupus erythematosus), severe psychological stress
• Mechanism: The telogen (resting) phase of hair growth predominates → premature shedding of the resting hair follicles → diffuse, nonscarring hair loss
• Clinical features
  • Hair density reduces by < 50%
  • Does not progress to complete baldness.
• Diagnosis
  • Clinical; scalp biopsy if uncertain (rarely necessary)
  • Hair-pluck test: ∼ 50% of hairs are in the telogen phase (normal: < 10%).
  • Tests to determine underlying condition
• Treatment: reassurance and manage underlying condition

Anagen effluvium

• Etiology
  • Drugs: systemic chemotherapy (esp. alkylating agents), anticoagulants, antidepressants, etc.
  • Radiation therapy to the scalp
• Mechanism: Interruption of the anagen (mitotic) phase → abrupt loss of ∼ 90% of hair (within days of exposure to the causative factor)

References:^{[9][10][11][12][13][14][15][16][17][18][19][20][21]}

Congenital circumscribed alopecia

• Temporal triangular alopecia
  • A well-defined oval/triangular patch of alopecia in the temporal part of the scalp
  • Seen before 5 years of age
  • Mimics alopecia areata and is differentiated from it by the presence of vellus hair and the absence of exclamation point hair
  • Treatment (if necessary): hair transplant/surgical excision
• Nevus sebaceus
  • A well-demarcated hamartomatous lesion predominantly composed of sebaceous glands
  • A solitary hairless, velvety, orange/tan plaque
  • Seen in infancy/early childhood
  • Risk of malignant degeneration (basal cell carcinoma, squamous cell carcinoma, etc.), esp. at puberty
  • Treatment: Surgical excision before puberty
• Aplasia cutis congenita
  • Intra-uterine developmental disruption of one/more layers of the scalp
  • A part of the scalp is missing at birth, which, on healing, causes scarred, hairless patch
  • Treatment
    • Small lesions: no treatment
    • Large lesions: surgical excision + primary closure/repair (with help of tissue expanders and skin flaps)

Acquired circumscribed alopecia

Alopecia areata

• Definition: Hair loss in well demarcated patches due to immune-mediated inflammation of hair follicles
• Epidemiology
  • Prevalence: 1 in 1000 people
  • Age: mostly in people < 30 years
  • Sex: ♂ = ♀
• Etiology
  • Immune mediated inflammation and disruption of anagen phase hair follicles → well-defined patches of nonscarring hair loss
  • A trigger factor (emotional stress, infections, pregnancy, etc.) may precede some cases
  • Family history in up to 20% of cases
• Clinical features
  • Abrupt onset (within weeks)
  • Smooth, circular, well defined patches of hair loss without scarring
  • Exclamation point hairs
  • Various patterns of distribution
    • Ophiasis: hair loss localized to the back and sides of the scalp
    • Sisiapho: sparing of the sides and back of the scalp
    • Extensive alopecia areata: hair loss affecting > 50% of the scalp
    • Alopecia universalis : All hair-bearing sites are affected (mimics telogen effluvium).
    • Alopecia totalis: Complete baldness
  • Nail involvement (up to 40% of cases): nail pitting, onycholysis, Beau lines, etc.
  • Other autoimmune disorders may be present (e.g., vitiligo, autoimmune disorders of the thryoid, etc.)
• Diagnostics
  • Usually clinical diagnosis
  • Biopsy, histology, and trichogram may be performed to confirm the diagnosis
• Differential diagnosis
  • Trichotillomania: Compulsive pulling out of one's own hair → ill-defined patchy hair loss and hairs of different lengths.
  • Loose anagen syndrome: Abnormal keratinization of the hair root → poor anchoring of the hair follicle to the scalp → hair falling out in clumps with minimal traction
  • Tinea capitis: The affected areas of scalp are scaly compared to the smooth hair loss of alopecia.
  • Secondary syphilis: patchy hair loss → moth-eaten appearance of scalp
  • Brocq pseudopelade
• Treatment
  • Intralesional steroids (triamcinolone)
  • Topical immunotherapy (DPCP (diphenylcyclopropenone) or SADBE (squaric acid dibutyl ester)
  • PUVA treatment (Psoralen + UVA)
• Prognosis: poor for alopecia universalis and totalis

Traction alopecia

• Definition: Hair loss due to chronic traction/tension on the hair follicles, mostly at the frontal and temporal scalp
• Etiology: Hairstyles involving tying the hair tightly
• Treatment
  • Avoid tight hairstyles
  • Topical minoxidil/steroids
  • Late stages: Hair transplantation/camouflaging techniques.

References:^{[21][22][23][24][25][26][27]}

• Definition: irreversible, chronic, diffuse hair loss that is triggered by chronic infection or disease
• Etiology: tuberculosis, leukemia, collagenosis, diabetes mellitus, neoplasms