Monilethrix

Etiology

Monilethrix is a hereditary hair disease transmitted in an autosomal dominant mode with high penetrance but a variable expression. It results from heterozygous mutations in hair keratin genes (KRT 81, KRT 83, KRT 86) on chr12q13, coding for the human basic type-II hair keratins hHb6 and hHb1.[4][5] An autosomal recessive form of monilethrix has been described, differing from classic monilethrix by rarely visible internodes and an inconstant periodicity. The suggestion is that the autosomal recessive monilethrix results from mutations in the desmoglein 4 gene (DSG4), the only desmoglein expressed in the keratinizing zone of the hair shaft cortex.[4]

Epidemiology

The prevalence and incidence are not known. No racial nor sex predilection is known for monilethrix, and it is not related to any particular hair color.

Pathophysiology

The exact mechanisms causing the periodic change in the diameter of the hair in monilethrix are still not clear.

Mutations in hair keratins genes KRT81, KRT83, or KRT86 most likely disrupt the keratin intermediate filaments formation in the hair shaft cortex.[4]

The hair breakage usually occurs in the internodal area where the medulla is absent. The thin hairs can sometimes break even inside the scalp. The consequence is that the broken hair shafts are caught in the infundibulum, causing a disruption of the outer root sheath and, thus, a constitution of a foreign body granuloma (clinically represented by red occipital papules).[1]

Monilethrix shows considerable variation in presentation, severity, and course, even within a single family. These phenotype variations have not been proved to correlate with the different genotypes of the disease [1], which raises the question of the influence of non-genetic factors in the onset of the disease.

History and Physical

Typically, the onset of monilethrix is during early childhood.[6][7] Affected patients usually have normal-appearing hair at birth, but several months later, they present with the complaint of short and fragile hairs that do not grow long enough to require a haircut.[8]

The clinical expression may vary from an almost normal scalp with few affected follicles to total alopecia. It is usually very characteristic, with diffuse hypotrichosis of the scalp and with extremely short dull and fragile hair that breaks easily, especially in the sites of friction such as the top of the head, the nape, and occipital areas.[1]

In severe forms, other hairy areas such as the eyelashes, the eyebrows, or the secondary sexual hairs may be involved.[9]

Perifollicular abnormalities are usually associated with the hair shaft fragility, ranging from perifollicular erythema to large hyperkeratotic follicular papules, most commonly found on the occiput. The hair fragility may as well be associated with trichorrhexis nodosa or other rare ectodermal symptoms such as syndactyly, cataracts, dental abnormalities, and nail abnormalities (koilonychia, brittle nails).[8]

Evaluation

The basis for a diagnosis of monilethrix is mostly upon clinical history and physical examination, and confirmation is usually by microscopy or trichoscopy.

Light microscopy of the hair reveals a beaded appearance with alternate constricted and normal segments placed about 0.7 to 1.0 mm apart.[1]

Trichoscopy represents a simple, non-invasive, and less time-consuming method that enables the practitioner to establish the diagnosis of monilethrix by revealing markedly higher rates of anagen hair as well as a characteristic “necklace” appearance.[6] High-magnification trichoscopy of the hair shows uniform elliptical dilations (nodes) and intermittent constrictions (internodes), causing regular variations in the diameter of the hair shaft and resulting in hair fragility at those points.[2][8] The nodes have a normal-hair diameter and a medulla, whereas the internodes usually have no medulla.[2]

Treatment / Management

To date, there is no known successful cure for this hair condition.[9] Topical minoxidil, oral acitretin, griseofulvin, systemic corticosteroids, and peeling ointments have shown to be effective in some cases. When used in low doses, oral minoxidil seems to be a promising and well-tolerated treatment for monilethrix.[10] Also, there have been reports of cases treated with N-acetyl cysteine, but symptoms recurred after an initial improvement.[2](B3)

Wigs may be a consideration for cosmetic purposes, but there have been suggestions that friction caused by wig adhesives may exacerbate hair loss.

The cornerstone of the management of monilethrix remains the avoidance of chemical and mechanical damage caused by excessive hair combing or washing and friction.[6][9] Hence, the education of the patient and his/her parents relating to lifestyle modification is necessary.(B3)

Differential Diagnosis

Some other hair shaft anomalies merit consideration in the differential diagnosis of monilethrix, such as pseudo-monilethrix, congenital alopecia, trichorrhexis invaginata, and ectodermal dysplasia.[9]

Prognosis

The prognosis of monilethrix considerably varies among affected individuals. Some cases remit spontaneously in adulthood, whereas most cases are persistent throughout life.[1][9] There have been suggestions that hair shine improvement and regrowth of apparently normal hair may occur in summer, with pregnancy and at the time of puberty.[2][9] Hormonal effects have also been suggested to play a role in recovery as there has been a report of clinical improvement in a patient after her first menstrual period.[11]

Complications

Monilethrix can predispose affected patients to low self-esteem and negative body perception, hence the need to assess its impact on the quality of life.[12] Other than psychological impact, complications related to the treatment modalities.