The case:

A healthy 9-year-old girl developed an asymptomatic eruption of discrete and confluent, 2 to 3 mm, hypopigmented papules in a linear pattern along the lines of Blaschko on the back of her left thigh and leg over the past 3 weeks. The lesions cleared without treatment 4 to 5 months later (Figure).

Diagnosis:

Lichen Striatus (LS)

Introduction

LS is a skin disease that commonly affects children between the ages of 4 months and 15 years. It is a benign condition with inflammatory hypopigmented, pink and occasionally purple papules, or lichenoid plaques that spread along the Blaschko lines.¹ These lines are named after German dermatologist Alfred Blaschko who discovered them in the early 20th century.² It was later appreciated that certain dermatological conditions such as LS follow the pattern of these lines.³

Discussion

LS is a benign dermatosis that is mostly seen in children. The condition has an abrupt onset, with erythematous, shiny, unilateral papules appearing along the limbs and neck in a characteristic Blaschkolinear pattern, a type of cutaneous mosaicism. The lesions coalesce to form continuous papules over days to weeks.⁴ They are most likely seen on the extremities, though rarely can be found on other parts of the body. Nails are involved in a few cases, leading to onychodystrophy and ridging.⁵ The exact etiology of LS has not yet been definitively understood. However, research has shown the predilection of a viral infection such as COVID-19, varicella, or influenza, and vaccination against hepatitis B and yellow fever to trigger an autoimmune response.^6,7

Differential diagnosis

Linear lichen planus may also present with similar lesions on the extremities; however, in lichen planus, the papules are intensely pruritic and violaceous as compared with LS (Table). Inflammatory linear verrucous epidermal nevus also presents with severe pruritic lesions that are congenital as compared with the acquired nature of LS.⁷ Incontinentia pigmenti or Bloch-Sulzberger syndrome also presents similarly; however, this X-linked disease has a multisystem involvement with various systemic manifestations.⁸ Linear cutaneous lupus erythematosus is another differential, which is very rare and can be confirmed only by cutaneous biopsy.⁹

Treatment

The usual course of LS is spontaneous resolution without treatment. The lesions resolve spontaneously in 6 months to 2 years.⁷ However, there might be residual scarring and hypopigmentation that may remain in certain cases.⁴ When the lesions are pruritic, low-potency steroids such as hydrocortisone cream and emollients may be tried. Immunomodulators such as tacrolimus and pimecrolimus may also be used to reduce the duration of the disease.^1,5

Conclusion

In our patient, the lesions resolved spontaneously after 4 to 5 months. Early diagnosis of the disease prevented mistreatment for the same.

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References:

1. Hajihoseini M, Eidy M, Molania T, Golpour M, Salehi M. Lichen striatus: review article. J Emerg Health Care. 2018;7(1):39-44. https://intjmi.com/article-1-300-en.html

2. Happle R. An early drawing of Blaschko's lines. Br J Dermatol. 1993;128(4): 464. https://doi.org/10.1111/j.1365-2133.1993.tb00212.x

3. Happle R. Lyonization and the lines of Blaschko. Hum Genet. 1985;70(3):200-206. doi:10.1007/BF00273442

4. Leung AKC, Lam JM, Barankin B, Leong KF. Lichen striatus: an updated review. Curr Pediatr Rev. Published online January 25, 2024. doi:10.2174/0115733963273945240101042423

5. Ruiz-Maldonado R, Violante-Morlock N. Liquen Estriado Dermatol Mex. 1971;15:27-41.

6. Belina ME, Sarver MM, Al-Rohil R, Fresco A. Lichen striatus post-COVID-19 vaccination. JAAD Case Rep. 2021;16:16-18. doi:10.1016/j.jdcr.2021.07.031

7. Herzum A, Viglizzo G, Gariazzo L, Ferro J, Vellone VG, Occella C. Lichen striatus after COVID-19. Clin Dermatol. 2022;40(6):744-746. doi:10.1016/j.clindermatol.2022.09.006

8. Cammarata-Scalisi F, Fusco F, Ursini MV. Incontinentia pigmenti. Actas Dermosifiliogr (Engl Ed). 2019;110(4):273-278. doi:10.1016/j.ad.2018.10.004

9. Lim D, Hatami A, Kokta V, Piram M. Linear cutaneous lupus erythematosus in children-report of two cases and review of the literature: a case report. SAGE Open Med Case Rep. 2020;8:2050313X20979206. doi:10.1177/2050313X20979206