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Naevi of Ota and Ito

Author: Vanessa Ngan, Staff Writer, 2003.

What are naevi of Ota, Ito and Hori?

A naevus (plural naevi, American spelling nevus, nevi) is a circumscribed and stable malformation of a component of the skin. Naevi are often present at birth, when they are often called birthmarks. Naevi composed of the pigment cells that produce melanin (melanocytes) are called melanocytic naevi.

Naevus of Ota, naevus of Ito and naevus of Hori are melanocytic naevi with slate-brown or blue/grey colouring. The naevus cells are found deep within the dermis, a form of dermal melanocytosis.

Dermal melanocytosis can also occur elsewhere on the body, including inside the mouth.

How does dermal melanocytosis arise, and who is at risk?

It is not known why dermal melanocytosis occurs. Specific mutations have been detected within the dermal melanocytes, most often GNAQ or GNA11. Researchers have suggested that hormones play a part in their development. The role of ultraviolet radiation is thought to be small, as it does not reach deep dermal melanocytes.

Naevus of Ota is much more common than naevus of Ito. These naevi are present at birth in 50% of cases but may appear during adolescence or adult life. Naevus of Hori is not present at birth and is therefore a form of acquired melanocytosis.

Naevi of Ota and Ito are most commonly found in Asian populations; 0.2-0.6% of Japanese people have nevi of Ota. They appear more frequently in females. Both forms of naevi are uncommon in Caucasians.

What are the signs, symptoms and complications of dermal melanocytosis?

In all forms of dermal melanocytosis:

How is the diagnosis of dermal melanocytosis made?

The diagnosis of dermal melanocytosis is usually made by observing typical discolouration of the skin. It is classified according to the site affected.

Some patients may undergo skin biopsy, which confirms the presence of melanocytes in the dermis.

Other skin conditions resulting in bluish or grey coloured skin may be considered. These include:

What treatments are available for melanocytosis?

Treatment of a melanocytosis includes:

If the eye is affected, regular eye examinations should be arranged to detect glaucoma. Any change in a naevus should be assessed by a dermatologist.

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