Don’t confuse rowan leaves with begonia leaves

Paediatric dermatology
Pigmentation disorder

Dr. Emmanuelle Bourrat

Saint-Louis Hospital

The clinical case
Now it's your turn!
Co-prescription and advice

Clinical case presentation

A 4-year-old boy was referred to dermatology for a workup of epilepsy evolving in a context of severe psychomotor delay (absence of walking and language) and polymalformative syndrome (major growth retardation, facial dysmorphia, microcephaly, cardiopathy).

There was a pigmentation disorder in the form of round or oval asymmetrical hypopigmented macules predominating on the trunk and the roots of the limbs. There were also large areas of barely cicatricial alopecia of the scalp, with no epidermal signs.

The cutaneous signs were present from birth, suggesting a neurocutaneous syndrome. A genetic workup was therefore proposed.

Your turn

What is your diagnosis?

Select 1 answer(s) from the following choices:

Tuberous sclerosis complex

Phylloid-type pigmentary mosaicism associated with mosaic trisomy 13

Incontinentia pigmenti

Waardenburg syndrome

Wrong answer!

Good answer!

Selected diagnosis

Tuberous sclerosis was not considered in this patient because of the dysmorphia, the polymalformative syndrome that was not suggestive, and the semiology of the white lesions: these did not resemble rowan leaves (oval, serrated leaves) but rather begonia leaves (asymmetric leaves).

This is therefore a type 3 phylloid (leaf-shaped) pigmentary mosaicism, easily distinguishable from other Blaschko line patterns such as linear lesions in narrow or wide bands (type 1a and b), checkerboard lesions (type 2), sheet lesions (type 4) or lateralized lesions (type 5).

Pigmentary mosaicism reflects a genetic (gene or chromosomal) abnormality of postzygotic origin, which it is important to try to identify when one or more associated extracutaneous anomalies are present. The phylloid pattern of a hypopigmented mosaicism is particularly suggestive of a mosaic chromosomal abnormality, most frequently involving chromosome 13.

Mosaic trisomy 13 was indeed identified in this child, explaining his phylloid depigmentation, vertex skin aplasia and polymalformative syndrome.

Explanation of wrong answers

The hypopigmented macules of tuberous sclerosis complex are variable in size but not Blaschko-linear. Their oval shape and crenellated border are classically compared to those of a rowan leaf.
Incontinentia pigmenti mainly affects girls (it is lethal in boys except in cases of postzygotic mutations). Late-stage (adult) skin lesions are hypochromic and atrophic, but the Blaschkoid pattern is linear and narrow (type 1a).
Waardenburg syndrome combines sensorineural deafness of varying severity with pigmentation anomalies affecting the eyes (iris heterochromia), hair (white forelock) and skin.

Treatment

Not applicable.

Message from the expert

Hypomelanosis of Ito is an obsolete term that should no longer be used. It referred to a group of heterogeneous genetic diseases featuring hypopigmentation along Blaschko lines (of any type) and various extracutaneous anomalies, including neurological disorders. These diseases now need to be better defined through in-depth genetic investigation.

References

^{Happle R. Phylloid hypomelanosis is closely related to mosaic trisomy 13.}^{Eur J Dermatol 2000; 10: 511-512}