DermatologyTier 2Disease (DEADMAN)

Cutaneous manifestations of inherited disorders - neurofibromatosis

Description

Neurofibromatosis type 1 produces characteristic, often diagnostic cutaneous findings - cafe-au-lait macules, axillary/inguinal freckling, cutaneous neurofibromas, and Lisch nodules (iris, not strictly cutaneous but part of the same diagnostic examination) - the skin findings are frequently what first raises diagnostic suspicion

One of the more common autosomal dominant single-gene disorders; cutaneous findings typically appear progressively through childhood, with cafe-au-lait macules often present from infancy and neurofibromas developing later (adolescence onward)

Biallelic NF1 inactivation (a "two-hit" tumour suppressor mechanism, similar in principle to other tumour suppressor-driven conditions) in Schwann cell precursors and melanocytes drives the characteristic pigmentary and tumour manifestations - explaining the combination of pigmentary changes (cafe-au-lait macules, freckling) alongside benign nerve sheath tumours (neurofibromas)

Diagnostic criteria (requiring 2+ of several features) include: >=6 cafe-au-lait macules (>=5mm prepubertal, >=15mm postpubertal), axillary or inguinal freckling, >=2 neurofibromas (or one plexiform neurofibroma), Lisch nodules (iris hamartomas), optic pathway glioma, a distinctive bony lesion, and a first-degree relative with NF1
The skin findings alone (sufficient cafe-au-lait macules plus freckling) are often adequate to make a confident clinical diagnosis without genetic testing in a typical presentation

Regular surveillance for the systemic complications NF1 predisposes to (optic pathway glioma in childhood, other CNS tumours, scoliosis, hypertension, learning difficulties) - the skin findings themselves generally require no specific treatment unless a neurofibroma is symptomatic/cosmetically concerning, in which case surgical removal is an option
Genetic counselling given autosomal dominant inheritance with high penetrance (though expressivity is variable)

Optic pathway glioma, plexiform neurofibroma (higher malignant transformation risk than cutaneous neurofibromas), scoliosis, learning difficulties, malignant peripheral nerve sheath tumour (a rare but serious complication)

The clinical diagnostic criteria for NF1 rely heavily on cutaneous/ophthalmological examination findings rather than requiring genetic testing in most cases - a thorough skin and eye examination in a child with multiple cafe-au-lait macules is often sufficient to establish the diagnosis confidently

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