80.4% NF1 Risk in Toddlers With Six or More Café-au-Lait Macules

Children under 29 months presenting with six or more café-au-lait macules (CALMs) carry an 80.4% risk of constitutional neurofibromatosis type 1 (NF1), according to age-adjusted cohort data discussed on the Society for Pediatric Dermatology's official podcast, Don't Be Rash.

The other side of that number matters just as much. Children older than 29 months with fewer than six macules, or with atypical lesions, carried a risk of just 0.9%. Host Andrew Krakowski, MD, spoke with Joseph Lam, MD, FRCPC, of BC Children's Hospital in Vancouver, about how to separate benign CALMs from early NF1 and its mimics — and the message for clinicians is that counting, timing and lesion morphology do most of the diagnostic work.

What do the 2021 consensus criteria require?

The revised 2021 international consensus criteria diagnose NF1 at two or more of seven features. CALMs count only at six or more lesions, each exceeding 5 mm before puberty or 15 mm after. The remaining criteria: intertriginous freckling, neurofibromas, Lisch nodules, optic pathway glioma, distinctive bone lesions, and a pathogenic NF1 variant or an affected parent.

Lam drew a basic histologic distinction that still trips up trainees. Unlike melanocytic nevi, CALMs reflect increased pigment production rather than an increased number of melanocytes. That difference underpins why the macules stay flat and sharply demarcated — and why their significance is about count and distribution, not cytology.

Why does age change the odds?

The Israeli cohort, with molecular testing performed in Alabama, provides the risk figures above. A separate St. Louis cohort found that most children with six or more typical CALMs met NF1 criteria by age 6 years.

For children below the threshold, the story is not over. Lam emphasized periodic full-skin examinations, because new spots and intertriginous freckling emerge with time and can tip a child over the diagnostic line. Lisch nodules also become more likely with age, so their absence on slit-lamp examination in an adolescent is genuinely reassuring.

Which mimics belong on the differential?

Several conditions reproduce pieces of the NF1 phenotype:

• Legius syndrome, caused by SPRED1 variants in the same RAS pathway, produces CALMs and intertriginous freckling without the full NF1 phenotype.
• Maculopapular cutaneous mastocytosis presents with raised, less sharply demarcated brown lesions; a positive Darier sign confirms the diagnosis.
• McCune-Albright syndrome, postzygotic in origin, pairs segmental CALMs with polyostotic fibrous dysplasia and endocrine hyperfunction, including precocious puberty and neonatal Cushing syndrome.
• Segmental pigmentary mosaicism is far more common than the segmental RASopathies, and mosaic NF1 can mimic a speckled lentiginous nevus.

When does genetic testing change management?

Genetic testing is now accepted in place of family history under the revised criteria, but Lam was pointed about its use: order it when the result changes management. A RASopathy panel including SPRED1 can separate NF1 from Legius syndrome, which spares families tumor surveillance that Legius does not require.

One pedigree pattern deserves attention. Affected siblings with unaffected parents should raise concern for constitutional mismatch repair deficiency, which carries implications well beyond skin findings.

For confirmed NF1, health supervision guidance centers on regular surveillance, including routine blood pressure checks — hypertension in NF1 can signal renal artery stenosis or pheochromocytoma, so the cuff is part of dermatologic follow-through.

The practical takeaway for the clinic: careful counting, age-adjusted risk estimates and targeted referral let clinicians reassure most families while identifying the children who need structured NF1 surveillance from the start.