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HamartomaBlaschko-linearICD-10 Q82.5

Naevus comedonicus

Comedonal naevus · naevus follicularis keratosus

Naevus comedonicus is a rare congenital hamartoma of the pilosebaceous unit characterised by grouped, dilated, keratin-plugged follicular openings arranged along the lines of Blaschko. Most cases are sporadic somatic-mosaic NEK9 mutations. The principal cutaneous distinction is from extensive comedonal acne; the principal clinical importance is the recognised though uncommon association with extracutaneous abnormalities — naevus comedonicus syndrome — including skeletal, neurological, ocular and dental anomalies.

CurrentLast reviewed 16 May 2026
Clinical image of Naevus comedonicus
Naevus comedonicus. Image sourced from DermNet New Zealand. Used under CC BY-NC-ND 4.0. No endorsement implied.

Genetics

  • Sporadic; somatic mosaic mutations in NEK9 (NIMA-related kinase 9) — characterised in 2016.
  • Less commonly somatic FGFR2 mutations.
  • Mosaic distribution along Blaschko lines reflects clonal origin from an ectodermal precursor.
  • Family history rare; transmission risk to offspring very low.

Clinical features

  • Groups of dilated keratin-plugged follicular openings.
  • Linear or arcuate / curvilinear configuration along Blaschko lines.
  • Often unilateral.
  • Onset: congenital or appears in childhood / adolescence; uncommon late-onset variants.
  • Sites: face, neck, trunk, limbs; rarely palms / soles.
  • Variable secondary changes:
    • Inflammation, cyst formation, scarring.
    • Secondary bacterial infection.
    • Recurrent abscess formation (Mosis-like in some).
  • Cosmetic and functional impact can be significant.

Naevus comedonicus syndrome

Recognised in ~10% of patients with naevus comedonicus when extracutaneous features are present:

  • Skeletal: ipsilateral limb-length discrepancy, syndactyly, polydactyly, vertebral anomalies.
  • CNS: developmental delay, seizures, neurological deficits.
  • Ocular: cataracts, coloboma.
  • Dental: hypodontia, supernumerary teeth.
  • Multidisciplinary surveillance indicated if syndromic features identified.

Differentials

  • Acne vulgaris (extensive comedonal) — bilateral, symmetric, age-of-onset typical, no Blaschko pattern.
  • Favre-Racouchot syndrome — bilateral periorbital comedones in solar-damaged skin.
  • Familial dyskeratotic comedones.
  • Epidermal naevus (linear / verrucous) — different histology.
  • Inflammatory linear verrucous epidermal naevus (ILVEN) — pruritic verrucous.
  • Linear lichen planus.
  • Steatocystoma multiplex — multiple soft cysts.
  • Trichoepithelioma / Brooke-Spiegler.

Investigations

  • Clinical diagnosis with characteristic Blaschko-linear comedones.
  • Skin biopsy if uncertain: dilated follicular structures with keratin plug; rudimentary sebaceous lobules.
  • If syndromic features suspected:
    • Spinal / skeletal X-rays.
    • Brain MRI for neurological symptoms.
    • Ophthalmology review.
    • Dental review.
  • Genetic testing (NEK9 from affected tissue) — specialist genetics centres.
  • Photograph for follow-up.

Management

  • Conservative:
    • Comedone extraction (sterile).
    • Topical retinoids (tretinoin 0.025-0.05% or adapalene 0.1%).
    • Topical salicylic acid 2-6%.
    • Topical antibiotics if secondary infection.
  • Oral: isotretinoin in severe / inflammatory variant (specialist; off-label).
  • Procedural / surgical:
    • CO2 / Er:YAG laser ablation for cosmetic / refractory cases.
    • Surgical excision with reconstruction for limited / cosmetically prominent lesions.
    • Tissue expansion for large lesions.
  • Multidisciplinary if syndromic — dermatology, paediatrics, neurology, ophthalmology, dental, genetics.
  • Counsel about benign cutaneous course; cosmetic considerations; possible recurrent inflammation requiring management.

References

  1. Levinsohn JL et al. Whole-exome sequencing reveals somatic mutations in NEK9 underlying nevus comedonicus. J Invest Dermatol. 2016;136:1737-1739.
  2. Tchernev G et al. Naevus comedonicus: an updated review. Dermatol Ther. 2013;26:493-499.
  3. Munro CS, Wilkie AOM. Epidermal mosaicism producing localised acne: somatic mutation in FGFR2. Lancet. 1998;352:704-705.
  4. Engber PB. The nevus comedonicus syndrome. Int J Dermatol. 1978;17:745-749.

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