An asymptomatic lesion with positive Darier sign on an infant


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A healthy 12-month-old infant girl presents with a yellowish-orange papule on the right upper extremity. Her mother first noticed this lesion approximately 6 months earlier. It has never bled, ulcerated, or formed blisters. The infant does not scratch the lesion nor appears otherwise bothered by it. However, when the lesion is rubbed, it appears to swell and turn bright red. On physical examination, there is a soft, oval-shaped, yellowish papule with a peripheral rim of erythema on the right extensor forearm. 

Mastocytosis describes a group of disorders that involve accumulation of mast cells in the skin and, in some cases, other organs of the body. Clinical presentation can occur at any age, from birth to middle age.1-5 The majority of cases,...

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Mastocytosis describes a group of disorders that involve accumulation of mast cells in the skin and, in some cases, other organs of the body. Clinical presentation can occur at any age, from birth to middle age.1-5 The majority of cases, however, occur before age 2 years.3 These lesions are congenital in up to one-quarter of pediatric cases. There is genetic correlation with c-KIT mutations in adult patients with mastocytosis, and similarly activating c-KIT mutations are found in pediatric cases of mastocytosis. Although this condition usually presents sporadically, familial cases are also reported in the literature.3

Mastocytosis is divided into two forms: cutaneous and systemic. Cutaneous mastocytosis can be categorized into four diagnoses: urticaria pigmentosa, solitary mastocytoma, diffuse cutaneous mastocytosis, and telangiectasia macularis eruptiva perstans.4,5 All of these subtypes can present with vesicular or vesicular variants that are suspected to be due to leakage of histamine or some other mast-cell-associated mediator. Cutaneous symptoms occur when these clusters of mast cells degranulate, releasing histamine, prostaglandin D2, heparin, tryptase, chymase, leukotrienes, and other mediators. This subsequently results in clinical signs and symptoms of flushing, blistering, and pruritus.1-2 Solitary mastocytoma is localized to one single lesion that contains a collection of mast cells in the skin.3

A physical examination, involving a Darier sign test, can assist with diagnosing cutaneous mastocytosis. This involves gently rubbing the affected area with a tongue blade or the blunt end of a pen or pencil to induce urtication. Within a few minutes, there should be localized erythema and urticarial wheals. This reaction may persist for 30 minutes to 1 hour and occasionally result in blistering.1-3 Although this does help confirm the diagnosis, it is possible that patients with mastocytosis will have a negative Darier sign test result.3

Mechanical irritation is not the only potential trigger of mast cell degranulation. Other documented triggers include exercise, heat, hot baths and beverages, cold exposure, stress, and exposure to sunlight. These patients should also avoid certain medications, such as aspirin, narcotics, dextromethorphan, nonsteroidal anti-inflammatory drugs, amphotericin B, thiamine, and topical polymyxin. Snakebites, bee stings, jellyfish stings, and iodine-containing contrast media may also trigger mast cell degranulation. In some patients, certain foods are also culprits—most common are strawberries, chocolate, tomatoes, citrus, egg white, ethanol, lobster, and crayfish.3

A diagnosis of solitary mastocytoma can often be made based on cutaneous morphology and presence of a Darier sign. However, atypical presentations can be confirmed by skin biopsy, which reveals a collection of mast cells in the dermis.1-3 Special immunohistochemical stains, such as Giemsa, toluidine blue, or tryptase antibodies, can provide further confirmation.1,2 Typically, solitary mastocytoma does not require further workup due to lack of systemic involvement. However, if the patient develops extensive cutaneous involvement or systemic involvement, other laboratory testing is available, including measurement of serum tryptase levels (a protease produced by mast cells) and urinary histamine levels.3

Because these lesions can urticate spontaneously, mastocytosis may be confused with urticaria. However, these lesions are so characteristic, the differential diagnosis is quite narrow. Of note, lesions such as those seen in urticarial pigmentosa will resolve but leave hyperpigmented macules in their place, which is atypical for urticaria. Occasionally, these may be confused with blistering conditions, since they can form overlying vesicles and bullae. Therefore, the differential diagnosis for blisters in children includes bullous arthropod bites, herpes simplex viral infection, bullous impetigo, autoimmune blistering diseases, epidermolysis bullosa, toxic epidermal necrolysis, and linear immunoglobulin A bullous dermatosis.1

Treatment for mastocytosis is primarily for symptom management. Patients should be counseled about the condition and its possible triggers. Typically, solitary mastocytomas do not require any treatment, especially if they are asymptomatic. For more generalized disease, nonsedating antihistamines, such as cetirizine, loratadine, and fexofenadine, are effective initial treatments. If there is severe or diffuse involvement, classic H1 antagonists, such as hydroxyzine and diphenhydramine, with or without H2 antagonists such as cimetidine, ranitidine, or famotidine for flushing and gastrointestinal symptoms, can also be helpful. Mastocytomas can also improve or resolve with a potent topical corticosteroid under occlusion, especially if these lesions are itchy or begin to form vesicles or bullae.1,2

In our case, given the localized involvement and lack of symptoms, the patient was prescribed topical triamcinolone ointment to be used only when symptomatic. The parents were counseled to return if new lesions appear. Typically, the prognosis for childhood mastocytosis is favorable; symptoms improve before adulthood in approximately 50% of patients.3

Tiffany Shih, MD, is a resident physician at the University of Minnesota in Minneapolis.


  1. Ramos-e-Silva M, Ribeiro de Castro MC. Myobacterial infections. In: Bolognia JL, Jorizzo JL, Schaffer JV, eds. Dermatology. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2012:1221-1242.
  2. Hansen’s disease. In: James WD, Berger TG, Elston DM, eds. Andrews’ Diseases of the Skin: Clinical Dermatology. 11th ed. Philadelphia, PA: Saunders Elsevier; 2011:334-344.
  3. Cutaneous tumors and tumor syndromes. In: Paller AS, Mancini AJ, eds. Hurwitz Clinical Pediatric Dermatology. 4th ed. Philadelphia, PA: Elsevier Saunders; 2011:206-209.
  4. Briley LD, Phillips CM. Cutaneous mastocytosis: a review focusing on the pediatric population. Clin Pediatr (Phila). 2008;47(8):757-761.
  5. Bulat V, Mihić LL, Situm M, et al. Most common clinical presentations of cutaneous mastocytosis. Acta Clin Croat. 2009;48(1):59-64.
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