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2021 NF1 Diagnostic Criteria and Legius Syndrome Differential

How clinicians measure cafe-au-lait macules, use non-sedated near-infrared OCT choroidal imaging in young children, and distinguish NF1 from benign SPRED1 Legius syndrome.

Primary Consensus: Legius et al., Genetics in Medicine 2021 (PMID: 34012067)
Dermatologist examining forearm pigment macules using a polarized handheld dermatoscope in a sunlit clinic

1. What Changed Between the 1987 NIH Rules and the 2021 Revision

2021 Consensus Update: The revised NF1 criteria added pathogenic NF1 gene variants as a standalone criterion, elevated optical coherence tomography (OCT) choroidal bright patches to equal diagnostic status alongside iris Lisch nodules, required bilateral or unilateral axillary/inguinal freckling evaluation, and mandated differentiation from SPRED1 Legius syndrome in pigment-only cases.

Under the 1987 rules, young children with six café-au-lait macules often spent years in diagnostic limbo waiting for second signs such as Lisch nodules or neurofibromas to appear. By incorporating near-infrared OCT choroidal abnormalities and high-sensitivity NF1 sequencing (Legius et al., 2021), clinicians can establish or exclude NF1 accurately in infancy or early childhood without unnecessary brain anesthesia scans.

01. CALM DIAMETER CUTOFF ( ≥6 SPOTS ) > 5 mm Pre-pubertal > 15 mm Post-pubertal Measure longest axis in room light 02. EYE & OPTIC PATHWAY (<8 YR) Slit-lamp + OCT ≥2 Lisch iris nodules or ≥2 OCT choroidal spots Annual visual acuity without sedation 03. CROWE SKINFOLD SIGN Axillary or groin Appears ages 3–5 yr Test SPRED1 if isolated 04. TIBIAL BOWING & ANNUAL BP Infant shin & annual BP Detect tibial dysplasia early; screen renal artery stenosis
Figure 1. Four pillars of initial pediatric NF1 evaluation: longest-axis macule measurement under ordinary room light, slit-lamp and OCT eye imaging, skinfold Crowe sign inspection, and infant tibial examination.

2. How Café-au-Lait Spots Are Counted — and What Does Not Count

Accurate dermatologic measurement prevents false referrals. Typical NF1 café-au-lait macules exhibit uniform light-to-medium brown pigmentation with smooth, well-demarcated ("coast of California") borders:

  • Pre-pubertal cutoff (>5 mm): At least six distinct macules measuring more than 5 millimeters across their longest axis under normal room illumination (Wood's lamp ultraviolet enhancement does not substitute for visible room-light counting).
  • Post-pubertal cutoff (>15 mm): At least six macules exceeding 15 millimeters in greatest diameter.
  • Lesions with irregular jagged borders ("coast of Maine"): Large segmental or jagged pigment patches warrant consideration of McCune-Albright syndrome or mosaic NF1 rather than classic constitutional NF1.

3. Separating NF1 from Legius Syndrome (SPRED1) and Constitutional MMR Deficiency

Roughly 2% to 8% of sporadic patients presenting solely with multiple café-au-lait macules and axillary/inguinal freckling carry a pathogenic variant in SPRED1 (chromosome 15q14), causing Legius syndrome. Distinguishing the two conditions transforms family counseling:

Feature Neurofibromatosis Type 1 (NF1) Legius Syndrome (SPRED1)
Café-au-lait macules & freckling Present in >95% of patients by age 5 Present; clinically indistinguishable on skin exam
Cutaneous or plexiform neurofibromas Common (plexiforms in 30%–50%) Absent (lipomas may occur in adults)
Optic pathway gliomas & Lisch nodules OPG in 15%–20%; Lisch/choroidal spots in >70% Absent (spares annual OPG eye surveillance)
Malignant nerve-sheath risk (MPNST) 8%–13% lifetime risk Not associated with neurogenic malignancy

In rare children with café-au-lait macules accompanied by consanguinity, hematologic malignancies, or high-grade brain tumors, multigene RASopathy panels should also exclude Constitutional Mismatch Repair Deficiency (CMMRD) (biallelic variants in MLH1, MSH2, MSH6, or PMS2).

Frequently Asked Clinical Questions

How many cafe-au-lait spots meet the 2021 NF1 criterion in a toddler?

Six or more smooth-bordered cafe-au-lait macules measuring greater than 5 millimeters across their longest axis in pre-pubertal individuals, or greater than 15 millimeters after puberty.

Why do doctors order both NF1 and SPRED1 genetic testing together?

Children who only have cafe-au-lait macules and skinfold freckling without tumors or eye findings may have Legius syndrome (SPRED1), which carries zero risk of neurofibromas or optic pathway gliomas.

Key Consensus Guidelines & Primary Sources

  1. Legius E, Messiaen L, Wolkenstein P, et al. Revised diagnostic criteria for neurofibromatosis type 1 and Legius syndrome: an international consensus recommendation. Genetics in Medicine. 2021;23(8):1506–1513. PubMed 34012067.
  2. Plotkin SR, Messiaen L, Legius E, et al. Updated diagnostic criteria and nomenclature for neurofibromatosis type 2 and schwannomatosis: an international consensus recommendation. Genetics in Medicine. 2022;24(9):1967–1977. PubMed 35674741.
  3. Gross AM, Wolters PL, Dombi E, et al. Selumetinib in children with inoperable plexiform neurofibromas (SPRINT Phase II). New England Journal of Medicine. 2020;382(15):1430–1442. PubMed 32187457.
  4. Moertel CL, Hirbe AC, Shuhaiber HH, et al. ReNeu: A pivotal phase IIb trial of mirdametinib in adults and children with symptomatic neurofibromatosis type 1-associated plexiform neurofibroma. Journal of Clinical Oncology. 2025;43(7):758–769. PubMed 39514828.
  5. Miller DT, Freedenberg D, Schorry E, et al. Health supervision for children with neurofibromatosis type 1 (American Academy of Pediatrics). Pediatrics. 2019;143(5):e20190660. PubMed 30988031.