Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2025;15(3):5544 1 Sparse Brittle Hair and Bilateral Temporal Alopecia in a Child Eduardo Rozas-Muñoz1, Jaime Piquero-Casals2, Juan Andres Madariaga3, Juan-Francisco Mir-Bonafé4 1 Department of Dermatology, Hospital San Pablo, Coquimbo, Chile 2 Department of Dermatology, Clínica dermatológica multidisciplinar Dermik, Barcelona 3 Department of Anatomic Pathology, Hospital San Pablo. Universidad Católica del Norte, Coquimbo, Chile 4 Department of Dermatology, Hospital Son Llàtzer, Palma de Mallorca, Spain Citation: Rozas-Muñoz E, Piquero-Casals J, Madariaga JA, Mir-Bonafé JF. Sparse Brittle Hair and Bilateral Temporal Alopecia in a Child. Dermatol Pract Concept. 2025;15(3):5544. DOI: https://doi.org/10.5826/dpc.1503a5544 Accepted: April 2, 2025; Published: July 2025 Copyright: ©2025 Rozas-Muñoz et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Eduardo Rozas-Muñoz, MD, Department of Dermatology, Hospital San Pablo Avenida Videla S/N, 1780000 -Coquimbo. Chile. E-Mail: docrozas@yahoo.com Case Presentation A healthy 2-year-old boy, the second child of nonconsan- guineous parents, presented with sparse, brittle hair and alopecia affecting the bilateral temporal and parietal scalp since he was 2 months old (Figure 1). Both parents had nor- mal hair; however, his 9-year-old sister experienced a similar condition that appeared to resolve spontaneously. Dermos- copy revealed regular constrictions in the hair shafts, giv- ing a beaded appearance. Hair microscopy showed beaded nodes at regular intervals with a reduced central dark me- dulla in the constricted areas. A diagnosis of monilethrix was made. Teaching Point Monilethrix is a rare hair shaft disorder, typically inherited in an autosomal dominant pattern. It is caused by mutations in genes encoding hair shaft proteins (KRT81, KRT83, KRT86, and desmoglein), leading to abnormal medulla formation, which results in hair thinning, fragility, and breakage [1]. Clinically, monilethrix is characterized by brittle, fragile hair and often sparse hair density, accompanied by patchy alo- pecia with variable distribution. The clinical presentation is remarkably polymorphic, even among members of the same family carrying the same genetic mutation. While some in- dividuals may exhibit only fine, sparse hair, others may develop extensive alopecia from an early age. Additional features such as follicular keratosis may be observed, partic- ularly on the scalp, neck, and extremities. The severity of the condition can vary over time, often being more pronounced during childhood and improving with age. In many cases, symptoms tend to improve or even resolve spontaneously in adulthood. There is no definitive treatment; however, sup- portive measures and avoiding trauma to the hair may help reduce breakage. 2 Image Letter | Dermatol Pract Concept. 2025;15(3):5544 Reference 1. Ortner-Tobider D, Trafoier T, Moosbrugger-Martinz V, Tollinger S, Gruber R, Schmuth M. Keratin variants in monilethrix. Br J Dermatol. 2024 Nov 18;191(6):863-864. DOI: 10.1093/bjd /ljae340. PMID: 39192774. Figure 1. Sparse, brittle hair and patchy alopecia in a 2-year-old boy with monilethrix, showing involvement of the temporal and parietal scalp.