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Clinical Handbook › Myths & Medical Glossary

Common Neurofibromatosis Misconceptions and Plain-Language Glossary

Correcting persistent historical myths—including Proteus syndrome misattribution—and translating radiology, genetics, and pathology terminology into clear clinical language.

Archive Heritage Chapter · Continuing nfcol.net's Historical Mitos & Vocabulario Sections
Neuropathologist examining nerve-sheath histology through a binocular laboratory microscope

1. Six Persistent Myths Corrected by Modern Evidence

Historical Clarification: Joseph Merrick ("The Elephant Man") did not have Neurofibromatosis Type 1; DNA sequencing of his skeletal remains in 2011 confirmed mosaic AKT1 Proteus syndrome, a completely unrelated overgrowth disorder.
Common Myth Clinical & Molecular Reality
"NF1 was 'The Elephant Man's disease.'" Disproven decades ago and molecularly closed in 2011 (NEJM): Merrick had Proteus syndrome (AKT1 mosaicism). Retiring this outdated label prevents severe stigma for newly diagnosed families.
"Mild NF1 can progress into NF2." Impossible—NF1 (chromosome 17) and NF2-related schwannomatosis (chromosome 22) are separate genetic entities from conception.
"Counting new café-au-lait spots measures disease progression." Spot count serves solely as an initial diagnostic clue; having 25 spots carries no higher tumor risk than having 6 spots.
"All neurofibromas are cancerous." Neurofibromas and schwannomas are histologically benign (WHO Grade 1) peripheral nerve-sheath tumors; only a subset of deep plexiform neurofibromas carries an 8%–13% lifetime risk of malignant transformation.
"NF can skip a generation silently in NF1." Classic constitutional NF1 exhibits ~100% penetrance by adulthood (an adult who did not inherit the parent's NF1 variant cannot pass it to grandchildren). Apparent "skipping" occurs mainly in incomplete-penetrance LZTR1 schwannomatosis or mild parental mosaicism.

2. Clinical Glossary of Genetics, Eye, and MRI Terms

  • ANNUBP (Atypical Neurofibromatous Neoplasm of Uncertain Biologic Potential): Borderline/premalignant lesion arising within a plexiform neurofibroma (often showing CDKN2A/B loss), curable by conservative nerve-sparing surgical excision before progressing to MPNST.
  • Choroidal Abnormalities (Bright Patches): Asymptomatic ovoid microvascular/melanocytic proliferations in the choroid detected painlessly by near-infrared OCT; included in the 2021 NF1 diagnostic criteria.
  • Crowe Sign: Cluster of small 1–3 mm freckle-like macules in axillary (armpit) or inguinal (groin) skinfolds unexposed to ultraviolet light.
  • Dural Ectasia: Widening or scalloping of the spinal dural sac seen on NF1 spine MRI; usually benign unless associated with dystrophic scoliosis or lateral meningocele.
  • FASI / UBOs (Focal Areas of Signal Intensity): Bright spots on pediatric T2/FLAIR brain MRI (basal ganglia, cerebellum, brainstem) seen in >60% of children with NF1; benign myelin vacuolization areas that are not tumors, require zero treatment, and typically fade by late adolescence.
  • Lisch Nodules: Benign pigmented hamartomas on the surface of the iris seen via ophthalmic slit-lamp; they never impair vision.
  • Plexiform Neurofibroma (PN): Diffuse or nodular nerve-sheath tumor growing along the length of a nerve trunk or plexus, often congenital and responsive to oral MEK1/2 inhibitors.
  • STIR Volumetric MRI: Short-Tau Inversion Recovery fat-suppressed MRI sequence used as the gold standard to measure 3D plexiform tumor volume (≥20% reduction defines partial response).

Frequently Asked Clinical Questions

What are UBOs or FASI bright spots on a child's NF1 brain MRI?

Focal Areas of Signal Intensity (FASI, formerly called unidentified bright objects) are benign areas of intramyelinic edema seen on T2 brain MRI in most young children with NF1. They are not brain tumors, do not require biopsy or treatment, and naturally regress during adolescence.

Do iris Lisch nodules affect eyesight?

No. Lisch nodules are microscopic benign iris hamartomas used purely as a diagnostic sign under slit-lamp examination; they never reduce visual acuity or cause pain.

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.