Large/giant congenital melanocytic nevus

What it is

From: Orphanet

A rare skin hamartoma characterized by at least one pigmented skin lesion present at birth of more than 20 cm (large congenital melanocytic nevus; LCMN) or 40 cm (giant; GCMN) projected adult diameter. The primary lesion is composed of mutated melanocytes and often locally disorganized epidermal annexes or dermis, and presents with an elevated risk of malignant transformation to melanoma or, more rarely, other neoplasms in skin or central nervous system.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of skin pigmentation · Very frequent (99-80%)

An abnormality of the pigmentation of the skin.

Congenital giant melanocytic nevus · Very frequent (99-80%)

The giant congenital nevus is greater than 8 cm in size, pigmented and often hairy. A giant congenital nevus is smaller in infants and children, but it usually continues to grow with the child.

Nevus · Very frequent (99-80%)

A nevus is a type of hamartoma that is a circumscribed stable malformation of the skin.

Anhidrosis · Frequent (79-30%)

Inability to sweat.

Dry skin · Frequent (79-30%)

Skin characterized by the lack of natural or normal moisture.

Poor wound healing · Frequent (79-30%)

A reduced ability to heal cutaneous wounds.

Atypical behavior · Occasional (29-5%)

Atypical behavior is an abnormality in a person's actions that can be controlled or modulated by the will of the individual. While abnormal behaviors can be difficult to control, they are distinct from other abnormal actions that cannot be affected by the individual's will.

Cutaneous melanoma · Occasional (29-5%)

The presence of a melanoma of the skin.

Headache · Occasional (29-5%)

Cephalgia, or pain sensed in various parts of the head, not confined to the area of distribution of any nerve.

Hydrocephalus · Occasional (29-5%)

Hydrocephalus is an active distension of the ventricular system of the brain resulting from inadequate passage of CSF from its point of production within the cerebral ventricles to its point of absorption into the systemic circulation.

Hypertrichosis · Occasional (29-5%)

Hypertrichosis is increased hair growth that is abnormal in quantity or location.

Increased intracranial pressure · Occasional (29-5%)

An increase of the pressure inside the cranium (skull) and thereby in the brain tissue and cerebrospinal fluid.

Neurodevelopmental delay · Occasional (29-5%)

Neurodevelopmental delay (NDD) refers to delays in the maturation of the brain and central nervous system; infants and young children with NDD may experience delays in the development of one or more skills including gross motor abilities, fine-motor coordination, language abilities and ability to solve increasingly complex problems.

Pruritus · Occasional (29-5%)

Pruritus is an itch or a sensation that makes a person want to scratch. This term refers to an abnormally increased disposition to experience pruritus.

Other findings in the same source

From: Orphanet

Additional reported features include Seizure (Occasional (29-5%)); Spinal cord compression (Occasional (29-5%)); Subcutaneous nodule (Occasional (29-5%)); Hypopigmented skin patches (Occasional (29-5%)); Cryptorchidism (Very rare (<4-1%)); Premature thelarche (Very rare (<4-1%)); Hypophosphatemic rickets (Very rare (<4-1%)). This is a selected summary, not a complete description of the condition.

When it may begin

From: Orphanet

Infancy; Neonatal

Inheritance in the source

From: Orphanet

Multigenic/multifactorial

Frequency and the population described

From: Orphanet

Point prevalence: 1-9 / 100 000; Europe; Value and class.

Which doctor should you see?

The suggested department for discussing Large/giant congenital melanocytic nevus is Dermatology, with a dermatologist as the relevant type of clinician. Dermatologist; paediatric services for children as appropriate.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which features of the skin, hair or nails distinguish the possibilities?
• Would photographs over time help document the changes?
• What should be expected from treatment, and how will irritation or other adverse effects be managed?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Large/giant congenital melanocytic nevus. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.