Pediatric Hair Disorders

An Atlas and Text, Third Edition

Juan Ferrando, Ramon Grimalt

• Publisher: CRC Press
• Year: 2016
• ISBN:
  9781498707930
• Edition: 3
• Topic: Medicina
• Subtopic: Teoria, pratica e riferimenti medici

Hair problems in child patients present a particular problem for clinicians: dermatologists, pediatricians, and family physicians can all worry they may not be up to date with what may be happening in the other specialties potentially involved. Written by authors with an international reputation, the new third edition of Pediatric Hair Disorders is full of clinical pictures, with a clear and concise text to help with the diagnosis of each entity. It will be helpful for all clinicians in training and in practice needing a quick and very visual resource to help with clinical diagnosis and to be confident they are using the best recommended techniques.

1

Hair Shaft Dysplasias

Hair shaft dysplasias are malformations of hair shafts. Most cases are congenital, hereditary or not; others are acquired (e.g., bubble hair). The malformations may involve a localized or generalized defect, but always follow a characteristic morphologic pattern [1,2]. The defects may be restricted to the hair or even constitute a diagnostic clue pointing to a genodermatosis (e.g., Netherton syndrome, trichothiodystrophy). Classification of hair shaft dysplasias is difficult but for practical purposes we accept the scheme shown in Table 1.1 [2,3].

Monilethrix (Beaded Hair)

Monilethrix is an autosomal dominant (AD) defect of the hair shaft characterized by short hair, only a few millimeters long and beaded. Breaking of the hair shaft occurs as soon as hair emerges from the ostium folliculorum due to narrowing of the shaft segments. Focal follicular hyperkeratosis and marked hypotrichosis may also be seen. Monilethrix generally affects individuals of different generations of the same family. The morphological defect is the periodic narrowing of the hair shaft that may be seen deep in hair follicles in biopsy specimens [4,5].

Genetics: Monilethrix is an AD hereditary defect caused by mutation of genes hHb1, hHb3, and hHb6 localized on chromosome (cr) 12q13 that encode diverse trichokeratins. We have recently reported a new family with a change in the nucleotide in heterozygosis at position 154 of exon1 of gene KRT81 (154 G > C). In the DNA sequence, this substitution involves a change of one amino acid in a protein (glycine for arginine at position 52) [6]. Interruption of keratin synthesis may be the cause of periodic variations of hair shaft diameter. Autosomal recessive (AR) cases have also been reported and are due to a gene mutation (18q) that encodes desmoglein 4 (DSG4), a situation that affects affinity for plakoglobin and alters hair shaft desmosomes [7].

Clinical diagnosis: The clinical picture includes diffuse hypotrichosis and short, fragile, and beaded hairs. Localized (occipital region) or generalized marked follicular hyperkeratosis may also be seen (Figure 1.1).

Optical microscopy: Alternating periodical beading (defect) and knots (normal hair shaft diameter) are characteristic aspects that may also be seen in dermoscopy (Figure 1.2). The hair shaft diameter is normal in the beaded segment of the hair shaft and the medulla is observed; these are not seen in the narrowed segments.

Scanning electron microscopy: Microscopic images are similar to those observed in optical microscopy; hair shaft fracture is evidenced in narrowed segments.

Trichoscopy: Dermoscopy is a useful tool for diagnosing hair shaft dysplasias. The typical “pearl necklace” image shows elliptical beading, regularly separated by narrowing segments where hair shaft fractures are usually observed. These findings are easily identified by dermoscopy—a simple method for a quick diagnosis [8,9] (Figure 1.3).

Histology: Intrafollicular hair shaft narrowing is observed.

TABLE 1.1

Classification of Hair Dysplasias

Dysplasias with Hair Fragility	Dysplasias with Little or No Hair Fragility
Monilethrix	Pili annulati
Pseudomonilethrix	Pseudopili annulati
Pili torti	Diffuse woolly hair
Menkes syndrome (kinky hair)	Woolly hair nevus
Trichorrexis invaginata (Netherton syndrome)	Acquired progressive kinking
Trichothiodystrophy	Diffuse partial woolly hair
Trichonodosis	Acquired partial curly hair
Distal trichorrhexis nodosa	Straight hair nevus
Proximal trichorrhexis nodosa	Pili canaliculi
Bubble hair
Loose anagen hair

FIGURE 1.1 Monilethrix. Diffuse hypotrichosis in occipital region is characteristic.

Pseudomonilethrix

Pseudomonilethrix is a rare AD defect characterized by hair fragility. Localized or diffuse hypothicosis and fake knots (irregular hair shaft flattening) occur as the result of compulsive and frequent combing of the hair. Follicular hyperkeratosis is not observed. Individuals of different generations within the same family may be affected [10,11]. This condition may be associated with trichorrexis nodosa and bubble hair.

FIGURE 1.2 Typical beading with alternating knots and narrowed segments is observed.

FIGURE 1.3 Elliptical beading with narrowed segments is seen on trichoscopy.

Genetics: Pseudomonilethrix is an AD defect. Specific genetic alterations have not been reported yet.

Clinical diagnosis: It is a familiar localized or diffuse hypotrichosis without follicular hyperkeratosis.

Optical microscopy: Rounded, normal appearing hairs with scarce and irregular oval or round nodules are present. Hair shaft narrowing is not observed (Figure 1.4).

Electron microscopy: What appear as nodules are actually flat segments of the hair shaft (Figure 1.5).

Trichoscopy: There are irregular distributed oval or round nodules without hair shaft narrowing segments and alternating of normal and wider segments of the hair shaft. No follicular hyperkeratosis is observed.

FIGURE 1.4 Pseudomonilethrix. Note round flattened nodules without hair shaft narrowing.

FIGURE 1.5 Hair shaft flattening is observed on scanning electron microscopy (SEM).

Acquired or Iatrogenic Pseudomonilethrix (Pseudopseudomonilethrix)

This defect is similar to pseudomonilethrix and arises from improper hair handling. It occurs when excessive pressure is applied to hair shafts during collection of samples from patients with monilethrix, woolly hair, and other conditions [12,13] (Figure 1.6). The same artifact is seen when a hair shaft is pressed between two slides (Figure 1.7).

FIGURE 1.6 Acquired pseudomonilethrix. The artifact in dysplastic hair is due to excessive pressure from removing hair with fingers, forceps, or tweezers.

FIGURE 1.7 Another view of acquired pseudomonilethrix.

Pili Torti

This disease involves braided hair with periodic ...