Master Keratoacanthoma with Picmonic for Physician Assistant

The most common clinical presentation of a KA is a skin-colored, single or solitary dome- or crater-shaped nodule with keratin-filled center. Size typically ranges from 1-2 cm. Less common KA clinical variants include: giant KAs greater than 2 cm, subungal KAs, mucosal KAs, keratoacanthoma centrifugum marginatum (KCM) with prominent horizontal growth patterns up to 20 cm, and disorders presenting with multiple KAs.

Most commonly seen in fair-skinned, middle-aged and elderly individuals with a peak incidence between the ages of 50 and 69.

Seen on sun-exposed areas of the skin. Most commonly found on the face, neck, arms and hands.

KAs are difficult to distinguish from squamous cell carcinoma (SCC) of the skin, because they share very similar histopathologic features. A lack of histopathologic features to definitively distinguish between the two has caused controversy surrounding KA being considered a variant of SCC or a distinct entity. KA is commonly referred to as low-grade SCC.

A rapid growth cycle over 4-6 weeks is a key distinguishing characteristic of KAs that helps differentiate the lesion from SCC.

Most KAs, if left untreated, have been shown to spontaneously involute and resolve within 6 months; however, some KAs persist for greater than one year-- further complicating the clinical distinction from SCC. While KAs are generally recognized as benign, treatment is recommended due to the association with SCC. Surgical excision, with the recommended surgical margins for SCC (at least 4 mm), is the first-line treatment for a solitary KA lesion--the most common clinical presentation of KA. This allows for both the histopathologic evaluation for diagnosis and the removal of the skin lesion.

Mohs micrographic surgery is a more complex and expensive surgical excision method that is tissue-sparing and allows for intraoperative assessment of tissue margins. When available, Mohs surgery is the preferred treatment for KAs in cosmetically sensitive locations such as the face. Due to this procedure being more costly and less widely available, it is typically reserved for patients in whom a tissue-sparing procedure is desired, or for lesions greater than 2 cm in diameter (giant KA--a less common KA variant).