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Case Report 
A preterm male child was born with a bald head, and a positive family history of similar complaints in the older sibling. The teeth and nails were normal. The rest of the physical examination and neurological examination were normal for their age. On examination, the child was bald with a few short, lustreless hairs present in the parietal region of the scalp [Figure 1]a. On trichoscopy, the tiger-tail appearance of hair was seen [Figure 1]b and a provisional diagnosis of monilethrix was made. The scalp was lightly scraped and smears were prepared. Both unstained and May-Grunwald-Giemsa-stained smears were examined microscopically. Smears showed a beaded appearance of the shaft of the hair with elliptical nodes having the thickness of a normal hair shaft separated by the abnormally constricted regions present at regular intervals [Figure 2]a and [Figure 2]b. Thus, a diagnosis of monilethrix was given.
Figure 1: (a) Child with bald scalp with few small lustreless hairs over parietal region. (b) Trichoscopy of scalp revealing tiger tail appearance of hair
Figure 2: (a) Cytological examination of the hair by scrape smears: Unstained Smear (Optical zoom: 400X, Digital zoom 1.10X) [Blue arrow: Internode, Red arrow: Node]. (b) Giemsa-stained scrape smear from scalp demonstrating beaded appearance of hair with internodes at regular interval (Optical zoom: 400X, Digital zoom 1.24X) Discussion Monilethrix is a rare hereditary condition affecting the shaft of the hair. It was described for the very first time in 1879 by Walter Smith as “a rare nodose condition of hair.”[1] The term monilethrix was given by Radcliffe Crocker has a Latin-Greek origin; monile (necklace) and thrix (hair), describing the beaded appearance of hair.[2]
It usually shows an autosomal dominant inheritance pattern with variable penetrance. Autosomal recessive cases have also been mentioned in the literature.[3],[4] A mutation in the genes encoding human basic hair keratins hHb1, hHb2, and hHb6, which are located on chromosome 12q11-q13 is the most common mutation leading to this condition.[3] Patients carrying a mutation in hHb1 have normal hair at birth, but they develop hair shaft abnormalities after a few months. Patients with mutations in hHb3 and hHb6 have a more severe form of the disease which affects the hair in eyebrows, eyelashes, and body hair, along with nail abnormality in the form of koilonychia. Recent studies showed the mutations associated with the autosomal dominant type of monilethrix are those in exon 1 and 7 of KRT86, KRT81, and KRT83 genes, whereas the autosomal recessive type is associated with a mutation in desmoglein-4.[1],[3],[4],[5]
A considerable variation is seen in the age of onset, the course of the disease, and the severity, which may or may not be related to the genotype. Patients usually have short, lustreless, brittle hair with perifollicular erythema, and follicular hyperkeratosis. The pathogenesis of the follicular hyperkeratosis is due to the fragile nature of the hair, which leads to the breaking of the thin hair shaft inside the scalp and the inability of the hair to grow out of the infundibulum, disrupting the outer root sheath. This gives rise to the formation of a foreign body granuloma and thus presents as perifollicular erythema. Monilethrix can be associated with other abnormalities like trichorrhexis nodosa, nail abnormalities like koilonychia, dental abnormalities, juvenile cataract, blepharitis, pannus, syndactyly, and growth retardation.[4]
Monilethrix has to be differentiated from other conditions with hair shaft abnormalities like pseudo-monilethrix, pili torti, and trichorrhexis nodosa, which can be achieved by cytological examination. Pseudomonilethrix is a genetic condition in which there is beaded appearance of hair but at irregular intervals. Pili torti is an autosomal condition in which the hair shaft is flattened and twisted at 180°. Trichorrhexis nodosa is an acquired hair shaft disorder due to mechanical trauma: the hair shaft breaks and has a brush-like appearance on microscopic examination.[6] The literature is replete with cases; however, none are found in the cytology literature.
There is no effective treatment available for monilethrix at present. Different treatment modalities like steroids, Minoxidil, biotin, acitretin, N-acetyl cysteine, griseofulvin, and oral contraceptives have been tried for this condition with improvement noted only in a few cases. Spontaneous improvement is noted in some patients post-puberty.[3]
To conclude, scrape cytology along with clinical and trichoscopic examination is needed to diagnose monilethrix cases and to differentiate them from pseudomonilethrix.
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The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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References 
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CheckDOI: 10.4103/joc.joc_25_22
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