A rare pediatric case of loose anagen hair syndrome

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A 13-year-old girl presented with a history of excessive hair shedding associated with thin, sparse scalp hair of inadequate length for the past 10 years. There was no history of scarring alopecia, systemic illness, or drug intake. On clinical examination, the scalp hair was blond, unruly, and uneven in length, with an overall reduced hair density [Figure 1a]. The hair pull test was strongly positive, with painless extraction of approximately 10–20 hairs. Light microscopic examination of hair mounts revealed a predominance of anagen hairs with characteristic deformities, including elongated, tapered, and occasionally twisted pigmented anagen bulbs [Figure 1b-c].

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Figure 1:

(a) Blonde, unruly, uneven in length, thin sparse hair, (b) Deformed pigmented anagen bulbs with tapered, twisted, or positioned at an acute angle to the long axis of the hair shaft on hair mount microscopy (10x), (c) Acute angled dystrophic anagen hair on hair mount microscopy (10x).

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Histopathological evaluation demonstrated a characteristic exaggerated cleft between the inner and outer root sheaths in the absence of perifollicular inflammation. Based on the clinical, trichoscopic, and histopathological findings, a diagnosis of loose anagen hair syndrome (LAS) was established. The patient was treated with topical minoxidil 5% lotion for six months; however, no significant clinical improvement was observed.

Loose anagen hair syndrome is a rare disorder of hair anchorage, typically presenting in childhood, and may occur sporadically or follow an autosomal dominant inheritance pattern. It results from mutations in the gene encoding companion layer keratin (K6HF), leading to premature keratinization of the inner root sheath and defective adhesion between the hair shaft cuticle and the inner root sheath.^[1] Clinically, LAS is classified into three phenotypes: type A, characterized by sparse hair that fails to grow long; type B, presenting with diffuse or patchy, unruly hair; and type C, seen predominantly in adults with normal-appearing hair but excessive shedding of loose anagen hairs.^[2] Microscopically, loose anagen hairs characteristically lack inner and outer root sheaths, show ruffling of the cuticle producing a “floppy sock” appearance, and exhibit deformed, pigmented anagen bulbs.^[3]

Tosti et al. initially proposed diagnostic criteria for LAS that included a positive hair pull test with painless extraction of at least 10 loose anagen hairs and the presence of more than 80% loose anagen hairs on trichogram.^[4] However, these criteria were considered overly stringent, particularly in mildly affected individuals. Subsequently, modified criteria were suggested, reducing the diagnostic threshold to ≥70% loose anagen hairs (modified Tosti criteria) or ≥50% (Cantatore-Francis and Orlow criteria).^[5] Although LAS often demonstrates spontaneous improvement with age, topical minoxidil has been reported to accelerate recovery in some patients, likely by prolonging the anagen phase and improving hair anchorage. However, responses may be variable, as observed in the present case.^[6]

Loose anagen hair syndrome is an uncommon but distinctive cause of chronic hair shedding in children, characterized by defective anagen hair anchorage and characteristic clinical, microscopic, and histopathological features. This case highlights the importance of recognizing LAS in children presenting with long-standing excessive shedding, sparse, unruly hair, and a painless positive hair pull test, to avoid misdiagnosis and unnecessary interventions. Although spontaneous improvement is common with advancing age, therapeutic response to topical minoxidil may be variable, underscoring the need for realistic counseling of patients and caregivers regarding prognosis. Early identification and appropriate reassurance remain central to the management of LAS.