KIT Gene, Mast Cell, Mastocytoma, Mastocytosis



  1. Jellerichs, Bradley
  2. Kim, Mary Elizabeth


ABSTRACT: This is a case study of a 9-month-old infant presenting with a blistering lesion on the left foot previously misdiagnosed as a benign birthmark. Pathology revealed cutaneous mastocytoma, which required no further intervention.


Article Content

Cutaneous mastocytosis (CM) is a rare disease characterized by an overproduction of mast cells. Childhood mastocytosis presents before the age of 15 years, but most cases (60%-80%) present during the first year of life (Heide et al., 2002). The prognosis is good, and symptoms tend to resolve spontaneously in late adolescence.



A 9-month-old female infant presented to the general dermatology clinic for an evaluation of a skin lesion on the foot. The mother had noticed the lesion at the age of 3 days. Twice in the intervening months, the lesion had formed a bulla, which then ruptured clear fluid (Figure 1). The lesion did not seem to cause pain or itch. There was no history of purulent discharge. The lesion had reportedly been diagnosed as a "birthmark" by the pediatric care provider. No topical or oral medication had been used. The lesion was noted to be growing at the same rate as the foot. Patient's medical history, family history, and prenatal course were unremarkable. The child was up-to-date on immunizations. Physical examination revealed a solitary 2 cm x 1 cm minimally elevated erythematous plaque with central shiny skin to the dorsum of the left foot with no active bulla (Figure 2). No other abnormalities were noted during a full skin examination. Shave biopsy was performed and sent to a children's hospital for expert consultation.

Figure 1 - Click to enlarge in new windowFIGURE 1. Bulla on the left foot. Photo taken by the mother.
Figure 2 - Click to enlarge in new windowFIGURE 2. Erythematous plaque on the left foot. Photo taken in the clinic.


Microscopic Findings

The sample was sent to the regional tertiary children's hospital for evaluation by pediatric pathology. Histopathology showed acral skin with elongation of the rete ridges of the epidermis. Within the superficial and mid-dermis, there was a proliferation of monotonous cells with round to oval nuclei; mild hyperchromasia; inconspicuous nucleoli; and abundant pale, faintly granular, cytoplasm. In the deeper dermis, the cells presented as single cells and thin trabeculae. Mitotic figures were inconspicuous. The cells showed strong, diffuse membranous positivity for C-KIT (CD117) and were negative for S100 and MARTI1. The lesion extended to the peripheral and deep margins.



After diagnosis was confirmed, no further intervention was required. Nursing interventions included counseling and reassurance. Mother was advised to avoid rubbing the area. Over time, the lesion is likely to flatten, the frequency of blistering episodes will decrease, and the lesion is likely to fully regress around the onset of puberty.



Mastocytosis is a group of disorders characterized by excessive mast cell accumulation in one or multiple tissues. It is subdivided into two forms: CM, which is limited to the skin, and systemic mastocytosis, which involves other organs. The World Health Organization further subdivides CM into four subtypes: urticaria pigmentosa (UP), diffuse CM, solitary mastocytoma, and telangiectasia macularis eruptiva perstans (Valent et al., 2001).


The symptoms of CM in children include macules, papules, and nodules. Erythema, edema, and bulla formation can occur and are associated with pruritus and dermographism. These symptoms are because of the presence of mast cells and the release of inflammatory mediators (Castells et al., 2011). The pathogenesis of pediatric CM is not well understood. In most cases, pediatric CM occurs spontaneously and is not hereditary. Pediatric CM is not known to show any correlations with other conditions, such as seasonal rhinitis, eczema, or asthma.


UP is the most common subtype of CM in children and adults. Lesions of UP are characterized by small yellow-tan to reddish-brown macules or slightly raised papules, which may be mistaken for freckles initially. In our patient, who only had one lesion and no apparent systemic symptoms, the best diagnosis is solitary mastocytoma (which is a different and less common subtype of CM).


The incidence of pediatric CM is low, affecting around one in 1,000 children (Heide et al., 2002). Children with CM are commonly diagnosed before the age of 2 years with one to three raised lesions on the trunk or extremities. Males and females are equally affected.


If a nurse suspects mast cell proliferation, the nurse can attempt to elicit the Darier sign, known to be positive in 95% of cases. Testing for Darier sign requires using a blunt instrument to rub the lesion for 10 seconds. The lesion is then observed for increased swelling or redness for 5 minutes (Heide et al., 2002).


If a pediatric patient is diagnosed with CM, the parent should be advised to properly care for the lesion if it ruptures. The ruptured lesion should be loosely covered with a bandage until it completely drains. Once drained, the area should be gently cleaned with soap and water and covered with a thin layer of petroleum jelly. The parent should monitor for signs of infection or purulent discharge. When the infant begins to walk, the parent should monitor for pain, which may warrant additional intervention.


In the described example, it is notable that the patient had been assigned an incorrect diagnosis. Diagnosis of mastocytosis can be challenging because the clinical presentation can be mild and may not come to the attention of parents or clinicians. Biopsies can also be difficult for pediatric patients to tolerate (Castells et al., 2011).


In some cases, treatment may be warranted because of pruritus or unacceptable cosmetic appearance. Oral antihistamines and topical immunomodulators can be prescribed. Tacrolimus and pimecrolimus may be indicated and have a side effect profile that is relatively benign (Sukesh et al., 2013). However, there are limited data on the use of these medications in infants.


The prognosis of CM is good. Ten percent of patients show complete resolution of symptoms, and 70% of patients show significant improvement in symptoms by the age of 10 years (Heide et al., 2002). The authors hope that publication of this interesting case helps educate dermatology nurses on the proper diagnosis and treatment of CM.




Castells M., Metcalfe D. D., & Escribano L. (2011). Diagnosis and treatment of cutaneous mastocytosis in children: Practical recommendations. American Journal of Clinical Dermatology, 12(4), 259-270.[Context Link]


Heide R., Tank B., & Oranje A. P. (2002). Mastocytosis in childhood. Pediatric Dermatology, 19(5), 375-381.[Context Link]


Sukesh M. S., Dandale A., Dhurat R., Sarkate A., & Ghate S. (2014). Case report: Solitary mastocytoma treated successfully with topical tacrolimus. F1000 Research, 3, 181.[Context Link]


Valent P., Horny H. P., Escribano L., Longley B. J., Li C. Y., Schwartz L. B., Marone G., Nunez R., Akin C., Sotlar K., Sperr W. R., Wolff K., Brunning R. D., Parwaresch R. M., Austen K. F., Lennert K., Metcalfe D. D., Vardiman J. W., & Bennett J. M. (2001). Diagnostic criteria and classification of mastocytosis: A consensus proposal. Leukemia Research, 25(7), 603-625. [Context Link]