CHAPTER 136

Disorders of the Hair and Scalp

Janice Ma, MD; Delphine J. Lee, MD, PhD, FAAD; and Ki-Young Yoo, MD

Disorders of the scalp may be congenital or acquired during childhood or adolescence. Conditions may be further classified according to the presence or absence of hair loss (alopecia), whether the hair loss is diffuse or circumscribed, and whether the hair loss results in scarring of the scalp.

Epidemiology

Scalp Disorders Without Associated Hair Loss

Among the congenital scalp disorders, caput succedaneum and cephalohematoma occur in an estimated of 1% of caesarean sections and 2% of vaginal deliveries via a cephalic position. Neonatal scalp abscess has an prevalence of 0.1% to 5.2%. Meanwhile, 85% of neonatal human herpesvirus infections occur at time of delivery and the scalp usually has the longest contact with the cervix, one of the sites for transmission of infection.

Among acquired scalp disorders, seborrheic dermatitis is most frequently seen in infants; however, it can occur in children and even adults, with an estimated prevalence of 5% across all groups (see Chapter 138). Atopic dermatitis is a common condition, affecting between 10% and 20% of school-age children in the United States (see Chapter 138). The prevalence of head lice (pediculosis capitis) is highest among children aged 3 to 11 years, with a propensity for affecting females and blacks more commonly. Scabies disproportionately affects resource-limited and crowded areas, with an estimated prevalence of 100 million people worldwide.

Scalp Disorders Associated With Hair Loss

Congenital scalp disorders leading to hair loss are uncommon compared with acquired scalp conditions. Nevus sebaceus is a congenital hairless lesion that mainly occurs on the face and scalp, occurring in about 3 of 1,000 neonates and affecting males and female newborns equally. Aplasia cutis congenita, the congenital absence of skin, presents in approximately 1 in 10,000 births.

Tinea capitis is a common acquired scalp disorder that can be associated with hair loss. Tinea capitis is a fungal infection of the scalp most often caused by the dermatophytes Microsporum canis or Trichophyton tonsurans. Tinea capitis affects primarily school-age children between the ages of 3 and 7 years and is less common in infants and postpubertal adolescents. Prevalence varies geographically but is estimated to be between 3% and 13% in the pediatric population. Boys are affected more often than girls with M canis, although both are affected equally in epidemics caused by T tonsurans. Black children have the highest rates of infection, although the reasons for this are unclear. Up to 60% of affected children are asymptomatic.

Alopecia areata is considered an autoimmune disorder targeting the hair follicles, with a prevalence of 0.1% to 0.2% in the United States, occurring equally in males and females. Although alopecia areata may develop at any age, it is rare before the age of 1 year, and 40% to 50% of cases of alopecia areata develop before the age of 21 years.

Traction alopecia is more commonly seen in females whose hairgrooming practices (eg, certain hairstyles, use of chemical relaxers combined with any pulling forces on the hair) result in excessive tension and trauma to the hair. Trichotillomania, or compulsive hair-pulling, may be seen at any age; however, onset is typically between the ages of 5 and 12 years (see Chapter 54). It affects females more often than males and children more than adults.

Pediatric discoid lupus erythematosus is rare, with a female predominance. Epidemiology data on the incidence of secondary syphilis in the pediatric population are limited. Meanwhile, the prevalence of Menkes disease (kinky hair syndrome) is estimated to be about 1 in 100,000 live births. Among the causes of diffuse hair loss in children (ie, telogen effluvium, anagen effluvium, and loose anagen syndrome), telogen effluvium is the most common.

Clinical Presentation

Children may present with specific symptoms, including localized baldness, pruritus, scaling, or inflammation (Box 136.1). Occasionally, lymphadenopathy, particularly in the occipital area, is the major presenting symptom.

Pathophysiology

An understanding of the physiology of the typical hair growth cycle helps in the evaluation of hair and scalp disorders. The average human scalp contains approximately 100,000 hairs. Individuals with blonde hair generally have 10% more hairs; those with red hair have 10% fewer. Healthy terminal hair grows an average of 0.3 mm (0.01 in) per day, or 1 cm (0.4 in) per month. Typical hair growth is a cyclic process composed of 3 stages. The anagen phase, the period of active hair growth, lasts for an average of 3 years (range: 2–6 years). Normally, about 85% to 90% of scalp hair is in this phase at any 1 time. The catagen phase, the transition period, lasts for about 10 to 14 days. The telogen phase, the final resting phase, lasts for about 3 to 4 months. About 13% of scalp hairs are in this phase at 1 time. The average individual loses about 100 to 150 telogen hairs per day. The typical hair cycle results in replacement of each scalp hair every 3 to 5 years.

Scalp Disorders Without Associated Hair Loss

Among the scalp disorders affecting newborns that are not associated with hair loss, both caput succedaneum and cephalohematoma are caused by birth trauma. Meanwhile, scalp abscess and herpesvirus are neonatal infections caused by rectovaginal bacterial flora and herpes simplex virus, respectively. The pathophysiology for atopic and seborrheic dermatitis is described in detail in Chapter 138. Head lice and scabies are infestations caused by Pediculus humanus capitis and Sarcoptes scabiei, respectively.

Scalp Disorders Associated With Hair Loss

Nevus sebaceus, a congenital scalp disorder that presents as a hairless plaque, is thought to be caused by noninherited mutations associated with a defect in the ectoderm, consequently resulting in hyperplasia of the epidermis and sebaceous glands. Aplasia cutis congenita occurs sporadically; however, familial cases have been reported. Aplasia cutis congenita is thought to be a result of many possible etiologies, including exposure to teratogens and trauma, and it can be an isolated defect or occur in association with other congenital defects such as cleft lip or palate, syndactyly, or multiple other genetic anomalies.

Tinea capitis is a communicable fungal infection and can be acquired via interpersonal contact, contact with infected animals, and fomites. There are 3 patterns of hair invasion. In endothrix infections (eg, T tonsurans), the fungus produces chains of spores within the hair shaft. In ectothrix infections (eg, M canis), spores are present around the exterior of the hair shaft. Favus, the most severe form of tinea capitis, demonstrates hyphae and air spaces within the hair shaft. This is usually caused by Trichophyton schoenleinii, a less common etiologic organism. Although dermatophytes have a relatively short incubation period (up to 3 weeks), they are viable in fomites for months. On close examination with dermoscopy, hairs may have a comma or zigzag appearance, with endothrix and ectothrix infections, respectively. Subcutaneous invasion in conjunction with an exaggerated host response can result in kerion, a boggy swelling of the scalp. Kerions are more commonly caused by a zoophilic dermatophyte, namely, M canis.

Pathophysiologic mechanisms of alopecia areata are not clearly known. One possible contributing factor is the aberrant expression of class 1 human leukocyte antigens on early anagen follicles, resulting in T lymphocyte recognition of these hairs, which are normally not recognized as foreign. There follows an immunologic attack causing premature transition to the telogen stage. The hairs then break easily at the surface of the scalp.

Traction alopecia and trichotillomania are caused by trauma to the hair. Discoid lupus erythematosus is an autoimmune condition thought to be multifactorial in etiology; the interplay of factors including genetic predisposition, sun exposure, and environmental toxins may lead to development of this condition. Secondary syphilis is caused by the bacterium Treponema pallidum, which can be transmitted during pregnancy through transplacental transmission, or through sexual contact. Treponema pallidum is not transmitted through human milk. Menkes disease is a congenital genetic disorder affecting copper uptake from the intestine, consequently resulting in copper deficiency. It is characterized by sparse kinky hair, failure to thrive, and neurodevelopmental deterioration. Telogen and anagen effluvium are 2 types of temporary hair shedding that occur at different growth stages of the hair cycle.

Differential Diagnosis

While some hair and scalp disorders can be easily recognized clinically, the differential diagnosis can be challenging at times.

Scalp Disorders Without Associated Hair Loss

These conditions are divided into those disorders seen most often in neonates and young infants and those seen more frequently in children and adolescents (Box 136.2).

Caput succedaneum, a generalized edema involving the soft tissues of the scalp, and cephalohematoma, a subperiosteal hematoma, are 2 of the most common lesions of the scalp that occur during the neonatal period, often caused by birth trauma. A cephalohematoma does not extend beyond the suture lines of the affected bone, which distinguishes it from caput succedaneum.

Other neonatal scalp conditions include infections such as scalp abscess and human herpesvirus infection. Scalp abscess occurs most commonly as a complication of scalp electrode placement. The infectious agents are usually flora of the cervix and vagina. Although most cases are self-limited, the abscess can be complicated by intracranial infection and/or sepsis. Patients who appear ill or have unstable vital signs may warrant additional workup, including blood cultures and/or neuroimaging based on clinical impression. Human herpesvirus infections of the scalp are not uncommon in neonates. Herpes lesions are typically vesicular, but petechial, purpuric, or bullous lesions may also be apparent. Skin lesions typically develop at 1 week after birth but may be present at birth or develop as late as 3 weeks later.

Seborrheic dermatitis and atopic dermatitis are the 2 most common diagnoses of scalp scaling among infants and children younger than 10 years. Seborrheic dermatitis is a red, scaly eruption that occurs mainly on the scalp (also known as cradle cap), face, and postauricular and intertriginous areas (see Chapter 138). It is often seen in infants and children younger than 2 years. Additionally, the scale, often termed dandruff in children 2 to 10 years of age, is usually associated with seborrheic dermatitis, and this is seen more in black children. Unlike atopic dermatitis, seborrheic dermatitis is generally non-pruritic. Occasionally, the inflammatory process is severe enough to result in diffuse hair loss. Psoriasis and Langerhans cell histiocytosis presenting on the scalp can mimic seborrheic dermatitis. Skin biopsy may be required for definitive diagnosis. Seborrheic dermatitis is often seen in conjunction with adenopathy of the head and neck without associated tinea infection.

^a May occur with or without associated hair loss.

Atopic dermatitis on the scalp is also characterized by erythema and scaling of the scalp, and it can overlap with seborrheic dermatitis. Atopic dermatitis on the scalp can be associated with significant pruritus with rubbing and scratching that result in the secondary effects of crusting and lichenification. Severe atopic and seborrheic dermatitis, as well as psoriasis, can result in pityriasis amiantacea (also known as tinea amiantacea, although it is not a fungal infection). Pityriasis amiantacea is a scalp condition that usually presents as localized, thick, adherent, and white or gray scale.

Head lice (pediculosis capitis) is an extremely common childhood infestation that affects girls more often than boys and is most common in children aged 3 to 11 years. Lice are spread by direct contact with infected individuals or infested clothing, combs, or other hair accessories. Pruritus is the primary symptom along with erythema and scaling, with secondary impetigo being common. The viable ova or nits may be visible as small, oval, tan to brown specks found most commonly attached to the hair above the ears and the nape of the neck. Hatched eggs are clear to white. Generally, only the ova clos-est to the scalp are viable. They are difficult to remove. Scabies, a pruritic infestation commonly seen in children, generally does not affect the scalp, except in infants, the elderly, and those who are immunocompromised. On the scalp of infants, 2- to 3-mm (0.08- to 0.1-in) erythematous papules are seen, with overlying excoriations and, often, secondary bacterial infection.

Scalp Disorders Associated With Hair Loss

Box 136.3 lists the common scalp disorders associated with hair loss. When evaluating hair loss in children, it is important to determine whether the loss is diffuse or circumscribed.

Nevus sebaceus is a benign, congenital growth characteristically presenting on the face or scalp. These lesions are characteristically hairless. In addition, they are usually solitary, well-circumscribed plaques on the scalp, yellow-orange in color, and ovoid to linear in shape. Nevus sebaceus can be associated with a small risk of malignant transformation, namely basal cell carcinoma, at a rate of less than 1% before the age of 18 years. Other benign growths within nevus sebaceus may also occur at a rate of approximately 1%. Therefore, regular monitoring or consideration of excision should be part of the management. Because of the relatively low risk and low metastatic potential, it is reasonable to postpone excision until later in life. Aplasia cutis congenita is a congenital skin defect with localized areas of epidermal, dermal, or subcutaneous tissue loss. Lesions can occur anywhere on the body, but most are found along the midline of the scalp. At birth, the lesions usually appear as punched out, round or oval defects that may have an overlying thin, glistening membrane. Erosion, ulceration, or a scar due to healing in utero can also be seen. A hair collar sign, or ring of long and coarse hair, may surround the lesion.

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