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A preteen girl who has had patchy bald spots since she was a baby was brought in by her parents for assessment.

On taking the girl's family history, clinicians observed that one of her parents was bald, and learned that her parent had the same history, although it was never diagnosed, reported Vincenzo Piccolo, MD, and Giuseppe Argenziano, MD, PhD, both of the University of Campania Luigi Vanvitelli in Naples, Italy, in .

"Clinical examination revealed sparse, unruly, fragile, and easily breakable hair," they wrote. Patches of thinning hair or complete hair loss were evident, particularly on the back of the girl's head, and hair follicle papules were scattered across her entire scalp.

A trichoscopic examination showed short hair in which typical dark elliptical nodes along the hair shaft were interspersed with paler elliptical nodes with no medulla. This gave the hair a beaded, necklace-like appearance, the authors noted.

Clinicians diagnosed the patient with monilethrix -- a rare nonsyndromic genotrichosis marked by hair shaft anomalies, which leads to hair fragility and hair loss.

Monilethrix is also known as necklace hair, nodosa hair, or beaded hair. In fact, the term "monilethrix" comes from the Latin word for necklace, "monile," and the Greek word for hair, "thrix."

This is usually passed on in an autosomal-dominant manner due to variants in KRT81, KRT83, or KRT86 that encode for type 2 hair keratins Hb1, Hb3, and Hb6, Piccolo and Argenziano explained. More rarely, a variation in DSG4 can cause recessive monilethrix. Recently, a nonsense variant in KRT31 was also found to be associated with autosomal-dominant monilethrix.

The condition interferes with keratin production, causing small nodes to develop within the hair shaft, which are "separated by repetitive thin internodal restrictions," the authors wrote. Because the patient's hair displayed typical features of monilethrix, and her father had the same disorder, the family decided not to undergo genetic testing.

As in this patient, typical presentation involves short and fragile hair with the characteristic beaded appearance, combined with erythematous follicular papules. It is marked by the appearance of "stubble" resulting from hair fragility, especially on the back of the scalp, which is typically exposed to friction.

While clinical presentation varies, the condition usually presents within a few months of birth, when terminal hairs replace lanugo hairs. This is when evidence of hypotrichosis, hair breakage, and patchy or complete hair loss may occur, although the alopecia rarely causes scarring.

When the condition is severe, hair loss may extend beyond the scalp to affect the eyelashes, eyebrows, armpits, limbs, or pubic hair. Some cases may also involve koilonychia, or cardiac and limb abnormalities in patients with Holt-Oram syndrome.

Trichoscopy plays an important role in diagnosing monilethrix, Piccolo and Argenziano noted, by "emphasizing the typical small nodes along the hair shaft periodically interrupted by regular constrictions of the hair with no medulla." Hair thickness varies from normal in the nodes to lower in the nonmedullated areas, which are more fragile; thus, broken hair will be evident where the shafts are thinner. Dermoscopic examination of keratotic papules may also reveal follicular plugs and yellow dots.

Trichoscopy is effective in distinguishing monilethrix from other differential diagnoses, the authors said. These include pili torti (twisting on a longitudinal axis), trichorrhexis nodosa (multiple thickened nodules of the hair shaft with normal internodes), and pseudomonolethrix (beading and flattening of the hair shaft with normal internodal thickness).

Monilethrix has been reported to improve on its own during puberty or pregnancy, the authors noted, although it rarely resolves completely. Patients should protect their hair from any trauma, such as weathering, curling, and perming, and exposure to sunlight, bleach, and dye.

Protective strategies represent "one of the most effective measures in this condition," Piccolo and Argenziano wrote. "Treatment is often unsuccessful, although improvement has been reported with use of systemic retinoids (such as acitretin) and topical minoxidil."

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