Café-au-lait macules and neurofibromatosis type 1

Meet the patient

A four-year-old is referred by her GP for "lots of brown birthmarks". On examination she has seven café-au-lait macules over 5 mm across the trunk, and faint freckling in both axillae. Her mother asks whether this is "just pigmentation" or something to worry about. [2]

Two questions are now live, and the whole topic exists to answer them: does she meet NF1 criteria? (she does — six or more CALMs plus freckling) and what must surveillance now catch before it harms her? (optic glioma in childhood, malignant change in a plexiform across life). Hold both and the management writes itself. [1]

The border tells you the syndrome

The single most useful bedside clue in a café-au-lait macule (CALM) is its border. NF1 CALMs are light brown, flat, oval and evenly pigmented with smooth, regular borders — the "coast of California". McCune-Albright CALMs have irregular, jagged borders — the "coast of Maine" — and follow Blaschko lines. [3]

Up to three CALMs are found in about 10 percent of the normal population, so a few macules alone do not equal NF1. Six or more CALMs (over 5 mm before puberty, over 15 mm after puberty) is the diagnostic threshold — and even then, the differential includes Legius syndrome, which mimics NF1 with CALMs and freckling but carries none of the tumour risk. [2]

The seven criteria — and the two-or-more rule

NF1 is clinical: two or more of seven criteria, no single one mandatory. The 2021 international consensus update retained the NIH 1988 framework, added the genetic criterion, and separated Legius syndrome. [2]

The number rule: two or more of seven. A parent with confirmed NF1 establishes criterion 7 in a child, but a child of an unaffected parent needs at least one criterion of their own plus a second feature. By age 8, about 97 percent of children who will meet criteria already do; by age 20, virtually 100 percent. [2]

Cutaneous manifestations — the four signs

Café-au-lait macules are light brown, flat, oval and evenly pigmented, present from birth or early childhood and increasing in number and size through childhood; they sit on the trunk and extremities, not the mucosa. [3]

Axillary and inguinal freckling (Crowe sign) — small 1–3 mm pigmented macules in the axillae, groin, base of neck and submammary folds — is pathognomonic for NF1 (not seen in Legius syndrome or other mimics) and appears around age 3–5. [3]

Cutaneous neurofibromas are soft, fleshy, pedunculated or dome-shaped pink or skin-coloured papules that appear at puberty and increase in number and size with age and pregnancy; they are benign, with no malignant potential. The buttonhole sign — the tumour invaginates through a dermal defect when pressed — is pathognomonic. [3]

The plexiform neurofibroma is the one that can kill. It is a large, diffuse, congenital tumour along a nerve that feels like a bag of worms, may cause overlying skin hypertrophy and hyperpigmentation, and carries a lifetime risk of malignant transformation to MPNST (malignant peripheral nerve sheath tumour) of roughly 10 percent. Surgical excision is difficult because it infiltrates along nerve trunks; selumetinib (a MEK inhibitor) is now FDA-approved for symptomatic unresectable plexiforms in children. [4]

Genetics — one gene, one brake off the RAS pathway

The NF1 gene sits on chromosome 17q11.2 and encodes neurofibromin, a large cytoplasmic protein whose central domain is a RAS-GTPase-activating protein (RAS-GAP) — it converts active RAS-GTP to inactive RAS-GDP. Loss-of-function mutations leave RAS stuck on, producing constitutive activation of the RAF-MEK-ERK (MAPK) and PI3K-AKT-mTOR pathways. [1]

Inheritance is autosomal dominant — 50 percent transmission from an affected parent, with 100 percent penetrance by adulthood but marked variable expressivity (a mildly affected parent can have a severely affected child). About 50 percent of cases are spontaneous (de novo) mutations with no family history. [1]

[1]

Pathophysiology — the RAS-MAPK pathway and its drug

Sustained RAS-MAPK signalling drives proliferation of neural-crest-derived cells — Schwann cells (neurofibromas, MPNST), melanocytes (CALMs, freckling) and neuronal or glial precursors. A second hit (Knudson) — somatic loss of the remaining NF1 allele — is required for tumour formation in the haploinsufficient cells, which explains the focal, multifocal nature of neurofibromas. Mast cells recruited by stem-cell-factor signalling infiltrate neurofibromas and drive growth and pruritus. [1][4]

The pathway is druggable. MEK inhibitors (selumetinib, trametinib, cobimetinib, binimetinib) suppress ERK phosphorylation downstream of RAS and shrink plexiform neurofibromas; cabozantinib is under investigation for MPNST. Large 17q11.2 microdeletions produce a more severe phenotype (earlier neurofibromas, higher MPNST risk, learning disability), while specific missense variants produce milder, CALM-predominant phenotypes. [4][8]

Systemic features — almost every organ is at risk

NF1 is a multisystem disorder, and the systemic burden dominates long-term morbidity more than the skin signs do. Systemic features fall into seven domains, each with its own surveillance. [5]

Neurological. Specific learning disability affects 40–60% of children — the commonest neurological morbidity — with ADHD in 30–40%, autism spectrum disorder in 15–25% and frank intellectual disability in 5–8%. Macrocephaly is seen in about 25%; seizures in 5–7%. Unidentified bright objects on T2/FLAIR MRI are seen in up to 70% of children, are typically asymptomatic and do not need biopsy. [5]

Ophthalmological. Optic pathway glioma (a juvenile pilocytic astrocytoma) develops in 15–20% of NF1 children, almost always before age 8, is bilateral in about half, and is usually indolent — only 30–50% of radiologically detected lesions are symptomatic. Lisch nodules (iris hamartomas) are present in over 90% of adults with NF1 and are a useful discriminator from Legius syndrome. [3]

Cardiovascular. Hypertension affects 15–25% — the three mechanisms are renal artery stenosis (commonest in children), phaeochromocytoma in 3–13% of adults, and coarctation (rare). A moya-moya-like cerebrovascular dysplasia may present with stroke. [5]

Skeletal. Sphenoid wing dysplasia (a distinctive osseous criterion), congenital tibial pseudarthrosis (a bowed tibia at birth that fractures), scoliosis (10–30%; the dystrophic type progresses fast and needs fusion), short stature and macrocephaly. [5]

Oncological — the malignancy burden. MPNST is the leading cause of NF1-related death (lifetime risk 8–13%; mean age 26–30; five-year survival 35–50%). JMML (juvenile myelomonocytic leukaemia) has a 200–500-fold increased incidence in NF1 children under 5. GIST is increased 30–50-fold (multifocal small-bowel, KIT-wildtype). Breast cancer risk is increased 3–5-fold in women under 50. [5]

Endocrine precocious puberty (especially with hypothalamic or chiasmal involvement) and phaeochromocytoma. Gastrointestinal GIST, periampullary neuroendocrine tumours and intestinal dysmotility from mesenteric plexiform disease round out the picture. [5]

Differential — CALMs are not all NF1

The discriminator line: NF1 CALMs are brown with smooth borders; tuberous sclerosis ash-leaf macules are white (hypopigmented); McCune-Albright CALMs are large and jagged. Hold all three and the bedside diagnosis is made. [1]

[3]

MPNST — the red flags you cannot miss

A plexiform neurofibroma that changes is malignant until proven otherwise. The single most sensitive feature of malignant transformation is new, persistent or nocturnal pain in a previously stable plexiform. Any red flag mandates urgent MRI with contrast, whole-body 18F-FDG PET-CT (an SUVmax over 3.5 raises MPNST suspicion), and image-guided core biopsy in an NF1 specialist centre. [4]

[4]

Management and surveillance — lifelong and multidisciplinary

NF1 requires lifelong, multidisciplinary surveillance coordinated through a specialist NF1 clinic — dermatology, clinical genetics, paediatrics or internal medicine, neurology, ophthalmology, orthopaedics, oncology and psychology. The schedule follows the 2019 AAP Health Supervision statement and the 2021 international consensus update. [7][2]

Children (birth to 18 years). At diagnosis: genetic counselling, baseline MRI brain and orbits, baseline ophthalmology and audiology, and a developmental assessment. Annually: blood pressure (every visit, every age), height, weight and head circumference, a full skin examination with plexiform mapping, a neurodevelopmental review, and annual ophthalmology (visual acuity, colour vision, fields, fundoscopy) until age 8, then 18-monthly — the single most important optic-glioma screening protocol. Reserve MRI for symptomatic patients (new visual loss, proptosis, abnormal visual-evoked potentials). [3][7]

Adults (18 years and older). Annually: blood pressure, full skin examination, a brief neurological review and BMI; breast examination in women (NF1 raises breast cancer risk 3–5-fold under age 50 — consider annual mammography from age 30 with MRI adjunct). A phaeochromocytoma screen (plasma free metanephrines) in any adult with hypertension, episodic spells or unexplained tachycardia. Plexiform surveillance by examination every 6–12 months, with MRI of any symptomatic or enlarging lesion. [5]

Plexiform neurofibroma and MPNST — selumetinib and surgery

Plexiform neurofibromas are present in 30–50% of NF1 patients, often congenital, and may compress the airway, spinal cord, bowel, bladder or orbit. MPNST screening is a core surveillance task. [4]

Treatment of inoperable plexiform disease: selumetinib. The SPRINT phase II trial (Gross et al., NEJM 2020) showed that 70% of children had a 20% or greater volume reduction with durable responses; the FDA approved selumetinib in April 2020 for symptomatic inoperable plexiform neurofibromas in children aged 2 years and older, at 25 mg per square metre orally twice daily (about 50 mg per square metre per day) in 28-day cycles until progression or unacceptable toxicity. Common toxicities are acneiform rash, diarrhoea, nausea, CK elevation and asymptomatic LVEF reduction. [6][8]

Surgery and MPNST. Complete excision of a plexiform is rarely feasible; debulking relieves mass effect. MPNST itself is treated with wide surgical excision plus adjuvant radiotherapy, with doxorubicin and ifosfamide for unresectable or metastatic disease; five-year survival is 35–50%, so early detection is the strongest prognostic factor. [4]

Subtypes and related RASopathies

Generalised NF1 is the classic phenotype. Segmental (mosaic) NF1 — a post-zygotic mutation in one embryonic lineage — confines features to a body region in a Blaschkoid distribution; gonadal mosaicism means a segmental patient can still transmit full NF1, so pre-conception genetic counselling is mandatory. [3] Spinal NF1 produces dumbbell neurofibromas from spinal nerve roots that may cause radiculopathy or myelopathy. [5]

Optic pathway glioma is treated first-line with carboplatin and vincristine (or vinblastine) when symptomatic or progressive; radiotherapy is avoided in children under 5 because of the secondary-tumour risk. GIST, JMML and phaeochromocytoma complete the malignancy and endocrine picture, each managed in its own pathway. [5]

NF1 sits in the RASopathy family alongside Legius syndrome (SPRED1), Noonan syndrome (PTPN11 and others), cardiofaciocutaneous syndrome and Costello syndrome — all germline disorders of the RAS-MAPK pathway. [1]

Pregnancy in NF1

Pregnancy may accelerate the growth of cutaneous and plexiform neurofibromas under hormonal influence. Specific risks are rapid growth of a pre-existing plexiform, new hypertension (including an unmasked phaeochromocytoma), cerebrovascular complications and a higher caesarean rate from pelvic or sacral neurofibromas. Offer pre-conception genetic counselling and multidisciplinary antenatal care, and re-evaluate neurofibromas postpartum. [5]

Prognosis and disposition

Overall life expectancy is reduced to under 50 years, driven principally by malignancy (MPNST, glioma, breast cancer, JMML), vasculopathy and cardiovascular disease. Prognosis is set by which complications declare themselves — a patient with isolated CALMs and cutaneous neurofibromas fares far better than one with a plexiform that transforms. [5]

Most patients are managed in a specialist NF1 clinic with the multidisciplinary team above. The safety-net for every patient and family: new pain or growth in a plexiform is MPNST until proven otherwise — urgent MRI and PET-CT. [4]

Evidence and regional differences

The 2021 international consensus criteria (Legius et al., Genetics in Medicine) added the genetic criterion and separated Legius syndrome, and the 2019 AAP Health Supervision statement (Miller) anchors paediatric surveillance. The SPRINT trial (Gross et al., NEJM 2020) established selumetinib for inoperable plexiform disease. [2][6][7]

Where the evidence is weak: optimal MPNST surveillance in asymptomatic patients (whole-body MRI is emerging but not yet standard everywhere), and the role of MEK inhibitors in adults and in MPNST itself, remain under investigation. [4]

Exam pearls

[1]

Exam application bank (NEET-PG and INICET)

One-line answer

Neurofibromatosis type 1 is an autosomal-dominant RASopathy of the NF1 gene on chromosome 17 (neurofibromin, a RAS-GAP tumour suppressor), diagnosed by two or more of seven NIH criteria (six or more café-au-lait macules, axillary or inguinal freckling, neurofibromas or a plexiform, optic glioma, Lisch nodules, an osseous lesion, an affected first-degree relative). CALMs have smooth coast-of-California borders; Crowe freckling is pathognomonic; the plexiform neurofibroma carries a roughly 10% MPNST risk; selumetinib treats inoperable plexiform disease. [1]

Worked stems (answer without another resource)

Stem 1 — Classic presentation. Map symptoms to mechanism; name the first investigation and first treatment step with dose and route if drug therapy is standard. [1] Stem 2 — Unstable or complicated. List red flags that force immediate resuscitation, theatre, ICU, antidote or reperfusion — and what you do in the first 15 minutes. [1] Stem 3 — Atypical group. Elderly, pregnancy, child or immunocompromised: how presentation and thresholds change. [1] Stem 4 — Differential trap. Name the three closest mimics and one discriminator for each. [1] Stem 5 — Disposition. Who goes home with safety-netting, who is admitted, who needs HDU, ICU or theatre, and what follow-up is mandatory. [1]

Rapid viva checklist

1. Definition and classification
2. Pathophysiology chain
3. Bedside signs and criteria
4. Score with exact components
5. Emergency bundle
6. Definitive therapy with doses
7. Complications of disease and of treatment
8. Special populations
9. Guideline or trial name if classic
10. Three exam traps

Coverage self-check

If you cannot answer any stem above from this page alone, re-read the matching section — the page is intended to be self-sufficient for final-prof and NEET-PG/INICET questions on Café-au-lait macules and neurofibromatosis type 1. [1]

Ward-round test — three stems, thirty seconds each

Stem 1 — the four-year-old with seven brown birthmarks (answer)

The four-year-old with seven café-au-lait macules over 5 mm and bilateral axillary freckling. Does she meet NF1 criteria, and what surveillance does she now need? Model: She meets NF1 criteria already — six or more CALMs (criterion 1) plus axillary freckling, the pathognomonic Crowe sign (criterion 2) — two of seven, with smooth coast-of-California borders. Confirm with genetic counselling and an NF1 gene test if the diagnosis is uncertain (and rule out Legius syndrome if neurofibromas and Lisch nodules never appear). Surveillance: annual blood pressure (renal artery stenosis), annual dermatology with plexiform mapping, annual ophthalmology to age 8 then 18-monthly for optic pathway glioma, orthopaedic review for scoliosis and tibial dysplasia, and a developmental assessment. Reserve MRI brain for new visual loss or proptosis. [2]

Stem 2 — the plexiform that starts to hurt (answer)

A 28-year-old with a known plexiform neurofibroma of the right thigh develops unremitting nocturnal pain over three months, and the lesion feels firmer. What is the concern and the action? Model: New, persistent, nocturnal pain and a consistency change in a known plexiform neurofibroma are the most sensitive features of malignant transformation to MPNST. The action is urgent MRI with contrast of the lesion and whole-body 18F-FDG PET-CT (an SUVmax over 3.5 raises MPNST suspicion), then image-guided core biopsy in an NF1 specialist centre. Do not reassure or observe. If MPNST is confirmed, treat with wide surgical excision plus adjuvant radiotherapy, with doxorubicin and ifosfamide for unresectable disease — five-year survival is only 35–50%, so early detection is the strongest prognostic factor. [4]

Stem 3 — the brown macules that are not NF1 (answer)

A six-year-old has three large, jagged, unilateral brown macules on one flank and an X-ray shows a bowed femur. Does she have NF1? Model: No — the irregular, jagged coast-of-Maine borders and the bony lesion point to McCune-Albright syndrome (GNAS mosaic mutation), not NF1. McCune-Albright adds polyostotic fibrous dysplasia (the "shepherd's crook" femur) and endocrine hyperfunction (precocious puberty). NF1 CALMs are smooth (coast of California), and she has fewer than six anyway. The border is the bedside test that separates the two syndromes. [3]

The mantra: two or more of seven makes the diagnosis; slit-lamp and blood pressure every year; and any plexiform that changes is MPNST until the PET-CT says otherwise. [1][4]

References

1. [1]Tamura R. Current Understanding of Neurofibromatosis Type 1, 2, and Schwannomatosis Int J Mol Sci, 2021.PMID 34072574
2. [2]Legius E, Messiaen L, Wolkenstein P, et al. Revised diagnostic criteria for neurofibromatosis type 1 and Legius syndrome: an international consensus recommendation Genet Med, 2021.PMID 34012067
3. [3]Ly KI, Blakeley JO. The Diagnosis and Management of Neurofibromatosis Type 1 Med Clin North Am, 2019.PMID 31582003
4. [4]Fisher MJ, Blakeley JO, Weiss BD, et al. Management of neurofibromatosis type 1-associated plexiform neurofibromas Neuro Oncol, 2022.PMID 35657359
5. [5]Saleh M, Dib A, Beaini S, et al. Neurofibromatosis type 1 system-based manifestations and treatments: a review Neurol Sci, 2023.PMID 36826455
6. [6]Gross AM, Wolters PL, Dombi E, et al. Selumetinib in Children with Inoperable Plexiform Neurofibromas N Engl J Med, 2020.PMID 32187457
7. [7]Miller DT; Committee on Genetics. Health Supervision for Children With Neurofibromatosis Type 1 Pediatrics, 2019.PMID 31010905
8. [8]Anderson MK, Johnson M, Thornburg L, et al. A Review of Selumetinib in the Treatment of Neurofibromatosis Type 1-Related Plexiform Neurofibromas Ann Pharmacother, 2022.PMID 34541874