Crutchfield Dermatology Case-of-the-month header image

Case of the Month

A mother brings in her 18-month-old boy to clinic because she was concerned with bruises on the back of his right thigh. She first noticed them about 2 months ago and they have not resolved. She is also unaware of any trauma that may have caused them or be causing them. The child is otherwise healthy

bruise leg

I asked for a tongue depressor and rubbed the lower “bruise” with the edge of the depressor for about 5 seconds and told the mother I was going to make a quick call and I’d be back in a few minutes.

When I returned, the lower bruise looked like this:

bruising on leg

What's Your Diagnosis?

Diagnosis: Urticaria Pigmentosa


Urticaria Pigmentosa is a benign neoplastic process of mast cells. In children, the condition manifests itself as papules, nodules, and tumors that urticate upon rubbing, often to the point of blistering. This urtication (as seen in our patients is called “Darrier sign”). In adults, it expresses itself as macules and papules accompanied by telangiectases (a.k.a. telangiectasia macularis eruptiva perstans). In adults, the lesions increase steadily in number and do not go away. The lesions of children tend to regress and disappear within months or longer.


Specialized stains for mast cells should be applied to sections of tissue from specimens of skin, the Leder stain being the most dramatic, coloring mast cells brisk red. If clinically there is evidence of disease of internal organs, a search should be undertaken for it-bone scan, for example, and aspiration biopsy of bone marrow.


The course of lesions of urticaria pigmentosa depends on the type(s) of lesions that constitute it. Children's papules, nodules, and blisters usually wane in weeks to months. By contrast, macules and papules in adults, called telangiectasia macularis eruptiva perstans, not only persist but become pro­gressively more numerous and widespread.


Urticaria pigmentosa, irrespec­tive of the patient's age at onset or its morphologic presentation, is a benign neoplasm composed of mast cells. Nodules of urticaria pigmentosa in children are characterized histopathologically by dense and diffuse infiltrates of mast cells. If such lesions have been rubbed prior to biopsy, the mast cells will be seen by conventional microscopy to have been joined by innumerable eosinophils. This is the consequence of the sudden release from mast cells of pre-packaged (in cytoplas­mic granules) eosinophilic chemotactic factor(s). In children, bullous lesions of urticaria pig­mentosa show a subepidermal blister in addition to the same fea­tures in the dermis that are present in nodules of the condition.

In adults, macular and papular lesions of telangiectasia macularis erupti­va perstans are characterized by sparse superficial perivascular infiltrates of mast cells around widely dilated venules of the superficial plexus, and those cells also are scattered in the interstitium of the upper part of the reticular der­mis. Mast cells usually are not found in the papillary dermis of the macular and papular expression of urticaria pigmentosa, and never are they present within the epidermis.

Although there are apparent morphologic differences in types of urticaria pig­mentosa as they present themselves in children and in adults, the process is fundamentally a benign neoplastic one of mast cells.


Sometimes the watch and wait approach is successful as many lesions will resolve on their own. Avoid activities that trigger. Talk to pediatrician about providing an EpiPen. For widespread macules and papules, antihistamines (H-1 and H-2 receptor antagonists) are valuable in alleviating pruritus. Dr. Crutchfield has had clinical success resolving the most troublesome lesions (usually 1-6 lesions) with overnight occlusion employing a class I steroid. Perform nightly for 2-4 week. If the first set is successful, the protocol can be repeated on other lesions. Orally admin­istered cromolyn sodium and UV phototherapy have also been helpful.

For severe, discrete persistent symptomatic nodules and tumors, surgical excision can be appropriate.

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Charles Crutchfield III M.D. Eagan Dermatologist

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Eagan, MN 55123 USA

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