Congenital melanocytic naevi and pigmentary birthmarks — formative SAQs

SAQ 1 (10 marks) — The six-week-old with a large dark birthmark on the back

Stem: A six-week-old girl is brought by her mother, who has noticed a large dark-brown patch covering most of the upper back since birth. The patch is well-defined, slightly raised, and covered with fine dark hair, and there are about a dozen smaller dark-brown spots scattered over the rest of the back and the shoulders. She was born at term, she is feeding and growing well, and her development is on track. On examination, the patch measures fourteen by sixteen centimetres over the thoracic spine, with the surrounding satellite nevi. The head circumference is on the fiftieth centile, the fontanelle is soft, and the neurological examination is normal. Outline your assessment, your diagnosis, and your management plan. [2] [6]

Model answer

Assessment and diagnosis (3 marks). This is a large congenital melanocytic naevus on the posterior axis with multiple satellite nevi. The lesion is a congenital melanocytic naevus on the morphological features — the brown colour, the well-defined border, the raised and the hairy surface, and the presence at the birth. The classification is by the projected adult size, and a fourteen-by-sixteen-centimetre lesion over the back, where the projected adult size is larger than the size in infancy, falls into the large category (projected adult size 20 cm and over). The dozen satellite nevi define the CMN syndrome pattern. The posterior-axis location (the thoracic spine) with the multiple satellites is the high-risk pattern for the neurocutaneous melanocytosis. [2] [1]

Risk stratification (3 marks). The melanoma risk in the CMN tracks the size, and the large and the giant CMN carry the elevated risk that is concentrated in the childhood and the adolescence, while the small and the medium CMN carry a risk close to the population risk. The neurocutaneous-melanocytosis risk is concentrated in the large or the giant posterior-axis CMN with the multiple satellites, so this child is in the group that warrants the consideration of the CNS imaging. The child is currently well, with a normal head circumference and neurology, which argues against the symptomatic neurocutaneous melanocytosis at the present. [1] [6]

Management (3 marks). The management is the referral to the specialist CMN service for the multidisciplinary assessment. The assessment includes the baseline photography and the dermoscopy, the consideration of the MRI of the brain and the spine for the neurocutaneous-melanocytosis screening (the high-risk pattern), and the establishment of the surveillance. The surgery and the laser are the individualised options for the cosmetic, the functional, or the difficult-to-monitor indication, not the routine prophylactic excision, because the prophylactic excision does not eliminate the melanoma risk. The family is counselled on the risk, the surveillance, the sun protection, and the change that must prompt the review. [3] [6]

Counselling and follow-up (1 mark). The family is counselled that the melanoma risk is elevated but not certain, that the surveillance is the early detection, and that the lesion will be monitored with the photography and the skin checks. The psychosocial support — the cosmetic burden, the anxiety, and the peer linkage — is the integral element. The safety-net is the change in the lesion, or the development of the headache, the seizure, or the developmental regression, that must prompt the urgent review. [3] [10]

SAQ 2 (10 marks) — The four-year-old with multiple cafe-au-lait macules

Stem: A four-year-old girl is referred to the paediatric clinic because her general practitioner noticed several flat, light-brown patches on her trunk at the four-year check. On examination, there are seven flat, evenly pigmented macules measuring 7 to 14 mm each, with smooth, sharp borders, scattered over the trunk and the limbs. Her growth is on the twenty-fifth centile, she is in her first year of school and managing well, and there is no relevant family history. Describe your assessment, the differential diagnosis, and the management plan. [10] [11]

Model answer

The recognition (2 marks). These are cafe-au-lait macules — the flat, evenly tan to light-brown patches with the smooth and the sharp border, present from the birth or the early childhood. The number is the key: this child has seven macules, and the NIH criterion for the neurofibromatosis type 1 is six or more cafe-au-lait macules over 5 mm before the puberty (over 15 mm after the puberty). This prepubertal child meets the criterion, so the assessment proceeds to the full NF1 work-up. [10]

The differential diagnosis (3 marks). The isolated cafe-au-lait macule is the benign finding and requires no investigation, but the six or more meet the NF1 criterion. The McCune-Albright macule is larger, fewer, and has the irregular coast-of-Maine border, and it accompanies the fibrous dysplasia and the endocrine overactivity such as the precocious puberty. The NF1 macule has the smooth, the sharp, the coast-of-California border. The distinguishing feature of the NF1 pattern here is the number (seven), the size (over 5 mm), and the regular border. The ash-leaf macule is the hypopigmented lesion of the tuberous sclerosis, not the hyperpigmented cafe-au-lait. [10] [11]

The assessment and investigations (3 marks). The full NF1 assessment follows. The slit-lamp examination looks for the Lisch nodules (the iris hamartomas). The skin is examined for the axillary and the inguinal freckling and the cutaneous neurofibromas. The developmental and the learning assessment is performed, because the NF1 affects the learning. The growth, the blood pressure, and the spine are examined. The family history is taken for the NF1. The genetic testing confirms the diagnosis when the clinical criteria are not met, but the diagnosis of the NF1 remains primarily clinical, based on the NIH criteria. [10]

The management and counselling (2 marks). If the NF1 is confirmed, the longitudinal care addresses the growth, the learning, the vasculopathy (the blood-pressure monitoring), the orthopaedic complications (the scoliosis, the pseudoarthrosis), and the tumour surveillance (the optic-pathway glioma). The genetic counselling is offered. If only the cafe-au-lait macules are found and no other NF1 feature develops over time, the diagnosis remains a possibility and the surveillance continues. The family is counselled in the plain language about the NF1, the variability, and the support, and the psychosocial and the educational support is the integral element. [10] [11]