The Darier’s sign is a quick diagnostic test for systemic mastocytosis (SM) in people who have skin lesions. While a positive Darier’s sign is more common in children than adults, it’s still a frequently used tool in the process of diagnosing SM.
What does it look like?
A positive Darier’s sign will cause a skin lesion to become itchy, swollen and red after it is stroked. Usually, it appears as a hive-like reaction, though it can also form a blister if the skin is irritated too much.
Why the Darier’s sign happens in mastocytosis
In patients with SM, certain areas of the skin might become infiltrated with mast cells, forming red or brown skin lesions. Rubbing the skin lesion can promote mast cell degranulation, which releases histamine into the skin and causes the Darier’s sign to appear.
How doctors test for the Darier’s sign
To test for the Darier’s sign, a doctor will stroke a skin lesion with a blunt object like a wooden tongue depressor, using mild to moderate pressure. They will generally do this about five times, then watch for a reaction.
A positive Darier’s sign is confirmed if, within a few minutes of stimulation, the lesion flares and a wheal appears on the skin. This can last anywhere from 30 minutes to several hours. If the reaction is uncomfortable for you, your provider may offer antihistamines to treat the reaction.
Read more about SM testing and diagnosis
The Darier’s sign is not a definitive test for SM. Both false negatives and false positives are possible, so this test should never be used on its own to confirm or rule out a diagnosis of SM. In addition, people can have SM without skin lesions, in which case testing for the Darier’s sign isn’t an option.
Risks of testing for the Darier’s sign
The Darier’s sign is often used as a safe and easy method of testing for SM. However, because the test directly causes mast cell activation, it can lead to a systemic response, which may include anaphylaxis. Therefore, you should never attempt to test for the Darier’s sign on your own — this test should only be performed under direct medical supervision.
Darier’s sign versus dermatographism
Dermatographism is a phenomenon in which the skin reacts by forming hive-like welts when scratched or rubbed. It’s a common and benign condition that is sometimes referred to as “skin writing.” Like the Darier’s sign, dermatographism is also caused by histamine release in the skin.
While the Darier’s sign and dermatographism can sometimes appear quite similar, they are not the same thing. The Darier’s sign is limited to the skin lesion, while dermatographism can create the appearance of a trail along the skin, including areas unaffected by disease. Individuals with SM can have either, both or neither of these conditions.
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