Monilethrix with variable expressivity.

Monilethrix is a rare autosomal dominant hair shaft disorder with variable expressivity. It usually presents with short broken scalp hairs and follicular hyperkeratosis. Light microscopy of hair reveals a beaded appearance. Here, we report the case of a 32-year-old male who presented with sparse hair and follicular keratotic papules in the absence of any family history.

INTRODUCTION

Monilethrix is a rare hair shaft disorder with structural defect resulting in increased fragility. It is usually transmitted in an autosomal dominant pattern. Affected individuals usually have normal appearing hair at birth, which is soon replaced by short, fragile and brittle hair. Perifollicular erythema and follicular hyperkeratosis are commonly observed. Hair microscopy shows elliptical nodes of normal thickness separated by abnormal constrictions resulting from defective cortical cell keratinization.

CASE REPORT

A 32-year-old male presented with decreased hair over the scalp and body since childhood. Patient was asymptomatic, and there was no history suggestive of impaired psychomotor development. He did not give any history of similar illness in his family members. Examination showed diffuse hair loss with short and brittle hairs over scalp, predominantly over the occipital region [Figure 1]. The moustache and pubic area also showed short broken hairs. Beard, axillary and body hairs were absent [Figure 2]. Follicular keratotic papules were seen over the occiput, nape of neck and extensor arms [Figure 3]. The eyes, nails and teeth were normal. Light microscopy of hair showed beaded appearance with elliptical nodes separated by narrower internodes thus establishing the diagnosis of monilethrix [Figure 4].

Figure 1

Predominant hair loss over occipital region

Figure 2

Absence of beard and axillary hair

Figure 3

Multiple follicular keratotic papules over the nape of neck

Figure 4

Beaded appearance of hair under light microscopy

DISCUSSION

Monilethrix is a rare structural hair shaft disorder. It was first described by Walter Smith in 1879 who called it ‘a rare nodose condition of the hair’ for which Radcliffe Crocker subsequently suggested the term monilethrix.[1] The word is derived from monile (Latin), which means necklace, and thrix (Greek), which means hair indicating the resemblance of the hair to a string of beads or a necklace. Hairs usually break at internodal area where cortex is defective and medulla is absent. The thinnest hairs can even break inside the scalp. The broken hair shafts do not find an easy way out of the infundibulum and they disrupt the outer root sheath. This gives rise to a kind of foreign body granuloma, a characteristic feature of the red occipital papules.

Autosomal dominant transmission has been demonstrated in numerous large pedigrees.[123] The gene appears to have high penetrance, but variable expressivity.[1] The alleged occurrence of normal carriers of the dominant gene has not been proven, as a parent with only 5% of abnormal follicles is easily passed as normal.[2] When determining the pattern of inheritance by the examination of relatives, it may be found that people thought to be unaffected transpire to have faint microscopic features, even if only on body hair.[1] Monilethrix has been associated with mutations in three keratin genes located on chromosome 12q13: hHb1, hHb3, and hHb6.[45] An autosomal recessive form of monilethrix was found to be caused by mutations in DSG4 while evaluating 12 Jewish families from Iraq, Iran, and Morocco, with microscopic findings of monilethrix, but with no evidence of vertical transmission.[6]

Monilethrix shows considerable variation in age of onset, severity, and course. There is not yet sufficient information to establish whether these variations are in part consistently correlated with different genotypes. There is, however, much variation even within the more commonly reported autosomal dominant form. Most commonly the hair is normal at birth and is progressively replaced by beaded and brittle hairs. Patients present with hair loss because of hair fragility that result in 1-2 cm long broken hairs. In mild cases the hair loss is localized to the occiput, but in severe cases the eyebrows, eyelashes, pubic, axillary and general body hair may be affected. Some of the broken stubs are observed to be projecting from keratotic follicular papules, especially on the occiput and nape of the neck. Light microscopy of hair shows a beaded appearance because of alternate zones of spindle like thickening and thinning placed about 0.7-1 mm apart. Patients may rarely have associated trichorrhexis nodosa, nail and teeth defects, retarded growth, and juvenile cataract. Some cases improve spontaneously after puberty though most persist throughout life. Avoidance of chemical and mechanical trauma may be helpful. Oral etretinate has been used with limited success.[7]

This case highlights the variable expression as our patient had a severe form of disease in spite of a negative family history, which may be the result of probable occurrence of normal carriers due to involvement of only a small number of hair follicles.