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Teen presents with hardened lesion on forearm
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A 15-year-old healthy male presented to the dermatology clinic for evaluation of a lesion on the right forearm. He first noticed it approximately 1 year ago. At that time, it was a hard, pink papule, which he thought was an insect bite. The lesion continued to enlarge over time. In the last month, it developed white papules within it. It has never drained. An attempt to perform an incision and drainage with his primary care provider 1 week before revealed blood rather than purulent drainage, with no improvement in the lesion. It is occasionally painful if bumped but otherwise asymptomatic.
His past medical history is significant for frequent pharyngeal streptococcal infections that resolved after tonsillectomy and adenoidectomy. There is no history of skin infections in the patient or first-degree family members. He participates in wrestling. On exam, there is a hard, mobile, subcutaneous plaque with central white papules and an irregular texture (Figure 1). When one side of the plaque is depressed downward, the opposite side elevates beneath the skin (Figure 2). A full skin examination is otherwise normal.
Can you spot the rash?
A. Epidermal inclusion cyst
B. Furuncle
C. Pilomatrixoma
D. Calcinosis cutis
E. Dermoid cyst
Pilomatrixomas, also known as pilomatricomas or calcifying epitheliomas of Malherbe, are common, benign cysts arising from the hair follicle that are composed of hair matrix cells (choice C). They typically occur in the first or second decade of life, although adults may develop them as well. The head and neck are the most common locations, but they can occur elsewhere. Sometimes, a preceding history of trauma is reported. Clinically, they present as well-circumscribed, hard, subcutaneous growths. Overlying skin may be smooth or have an irregular texture. Calcifications may appear as white papulonodules protruding outward. An overlying bluish or pink hue can be appreciated in some lesions. One study showed that most lesions were between 1 and 2 cm in size. Growth is usually slow over the course of months to years, although they can become inflamed with surprisingly rapid enlargement and erythema.
A mutation in beta-catenin, a protein in the Wnt signaling pathway, has been identified in many pilomatrixomas. Most are solitary lesions but rarely multiple lesions may be present. In these cases, associated syndromes should be considered, including Turner syndrome, Gardner syndrome, Kabuki syndrome, myotonic dystrophy or constitutional mismatch repair deficiency. Almost all reported patients with an associated syndrome had already been diagnosed with the primary syndrome at the time they developed their pilomatrixomas. In the absence of other abnormalities in the patient’s personal or family history, no additional workup is needed.
A clinical pearl that may aid in the diagnosis is the “teeter-totter” sign, where pushing on one end of the cyst causes the other end to lift. Another classic finding is the “tent” sign, where stretching the skin over the lesion reveals the uneven subcutaneous surface of the cyst. Ultrasound may help in the diagnosis of pilomatrixomas by demonstrating calcification, but this is not always present. Lesions may present as cystic or hypoechoic masses with some internal vascularity — a nonspecific finding. Histopathology is the gold standard for diagnosis, demonstrating a combination of basaloid cells, so-called “ghost” cells, and calcifications. Up to 25% of pilomatrixomas may also have pigmentation.
Pilomatrixomas do not typically resolve spontaneously. Definitive treatment requires surgical removal of the cyst. Recurrence is low. Rarely pilomatrixomas can undergo malignant transformation to pilomatrix carcinoma (<150 cases reported in the literature), and any recurrent lesions should be closely monitored.
Pilomatrixomas are frequently misdiagnosed clinically as other skin lesions. Dermoid cysts are congenital lesions that arise in embryonic fusion planes. Some are not recognized at birth and may be identified only later in childhood when they grow. These occur on only the face, scalp or spinal axis, and occur most commonly along the orbital ridge. Dermoid cysts may also have a bluish hue and can feel firm, though not typically as hard as a pilomatrixoma. Treatment is also surgical excision, and histopathology can easily distinguish between the two.
Epidermal inclusion cysts are typically seen after puberty but can arise in younger children as well. Sometimes erroneously called “sebaceous cysts,” these are epithelium-lined subcutaneous cysts. They can occur anywhere on the body, although they favor the head, neck, trunk and scrotum. They are typically mobile and may be somewhat firm, though again not as firm as a pilomatrixoma. Often a central punctum is visible, and white keratinaceous material can be expressed from the cyst. Surgical removal of the entire cyst lining is required for treatment, and they have a higher rate of recurrence.
Calcinosis cutis is a general term for calcium deposition in the skin. It may be seen in the context of trauma or inflammation of the skin, autoimmune diseases such as dermatomyositis or scleroderma, abnormal calcium or phosphorous metabolism or following IV infiltration. Lesions range from solitary to widespread, often depending on the underlying cause. Looking for associated conditions or history of trauma (eg, heel sticks) can help with the diagnosis. Treatment is typically challenging.
Furuncles typically arise over a period of a few days and are most commonly caused by bacteria such as Staphylococcus aureus. They often have overlying erythema or cellulitis. They are tender, warm and fluctuant on palpation. Smaller, uncomplicated furuncles may respond well to incision and drainage alone, although larger or more complicated infections may require antibiotics or packing.
When evaluating a subcutaneous growth in a child, particularly on the head and neck, pilomatrixoma is important to have on the differential. Its rocklike texture is a clue to the diagnosis. Unnecessary interventions and diagnostic procedures can be avoided if the correct diagnosis is made. Patients should be referred to a dermatologist or plastic surgeon for definitive treatment and removal of these lesions.
- References:
- Jones CD, et al. Am J Dermatopathol. 2018;doi:10.1097/DAD.0000000000001118.
- Lin SF, et al. J Clin Ultrasound. 2018;doi:10.1002/jcu.22517.
- Paller AS, et al. Hurwitz Clinical Pediatric Dermatology: A Textbook of Skin Disorders of Childhood and Adolescence. 5th ed. London: Elsevier; 2016.
- Richet C, et al. Pediatr Dermatol. 2018;doi:10.1111/pde.13564.
- For more information:
- Colleen H. Cotton, MD, is a pediatric dermatology fellow at The Children’s Hospital of Philadelphia. She can be reached at cottonch@email.chop.edu.
- Marissa J. Perman, MD, is an attending physician at The Children’s Hospital of Philadelphia.
Disclosures: Cotton and Perman report no relevant financial disclosures.