Monilethrix

A rare genodermatosis characterized by a hair shaft dysplasia resulting in hypotrichosis.

Epidemiology

The prevalence and incidence are not known.

Clinical description

Monilethrix has an early onset in infancy. Alopecia, associated with follicular hyperkeratosis and perifollicular erythema, can involve only the occiput and the nape of the neck or, in severe forms, the entire scalp, the eyebrows and eyelashes, and secondary hair. Infants show a characteristic hair shaft dysplasia: dystrophic constrictions regularly separated by elliptical nodes of normal thickness, giving a beaded appearance of affected hair. The thin internodal region shows a high propensity to break. In some cases, nail dystrophy (koilonychia) on fingers and toes has been reported. This symptomatic triad (moniliform hair, follicular hyperkeratosis and nail dystrophy), when associated with other ectodermal defects, such as as neurological, dental, and ophthalmological alterations, constitute the ''moniliform hair syndrome''.

Etiology

Four genes have been associated with monilethrix: KRT81, KRT83 and KRT86, coding for the type II hair keratins Hb1, Hb3 and Hb6, and are responsible for the autosomal dominant form of the disease. An autosomal recessive form has also been described in a few families, caused by mutations in the DSG4 gene, coding for the desmoglein 4 protein, also involved in hypotrichosis simplex (see this term) that has clinical overlap with monilethrix.

Diagnostic methods

A trichogram shows the characteristic moniliform hairs. Trichoscopy is another approach to detect the characteristic hair shaft dysplasia of monilethrix. An electron microscopy-based diagnostic test is available.

Differential diagnosis

Differential diagnosis includes pseudomonilethrix that presents with diffuse alopecia or alopecia limited to the occipital area. However, using trichogram analysis, pseudomoniletrix hair does not present with dystrophic constrictions but with flattened irregular beading.

Genetic counseling

In severe forms with alopecia and hyperkeratosis on the body, genetic counseling would be necessary.

Management and treatment

Treatment is disappointing. The best measure is to avoid the mechanical action of combing and brushing. Depilation only achieves repopulation with normal looking hair for a short while. Temporary improvement has been described with daily doses of 125 mg of griseofulvin, zinc-sulfate, X-ray depilation, and topical application of retinoid acid. There have also been improvements with the application of minoxidil and tretinoin, and with the administration of 0.5-1 mg/kg/day of etretinate.

Prognosis

The course of the localized form of monilethrix can be favorable with a reduction of hypotrichosis with time. In general, hypotrichosis improves with age, although remissions have been noted during puberty or pregnancy.