Crateriform nodule on a cyclist - Clinical Advisor

Crateriform nodule on a cyclist

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A 59-year-old Caucasian female presented to clinic with a crateriform nodule on the posterior right calf. She stated that it first appeared as a small, pimple-like lesion and grew rapidly over three weeks. It was currently approximately 1 cm in diameter. The patient reported being an avid biker and spending several hours daily riding in biker shorts with both her calves exposed. She denied any pain, tenderness, or bleeding, but she did note that the lesion had developed a keratotic core at the center. 



HOW TO TAKE THE POST-TEST: This Clinical Advisor CME activity consists of 4 articles. To obtain credit, you must also read Scaly plaques after 
onychomycosis therapy,
 Annular eruption on the lower leg
 and Enduring eruption of papules on the chest. Then take the post-test here.


Keratoacanthomas are often considered a variant of squamous cell carcinoma. There are some who consider these lesions benign tumors, or pseudomalignancies.1They typically present as a solitary, rapidly enlarging papule that erupts into a sharply well-circumscribed crateriform nodule with a central...

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Keratoacanthomas are often considered a variant of squamous cell carcinoma. There are some who consider these lesions benign tumors, or pseudomalignancies.1They typically present as a solitary, rapidly enlarging papule that erupts into a sharply well-circumscribed crateriform nodule with a central keratotic core in 3 to 8 weeks. 

Most keratoacanthomas span about 5 mm to 15 mm in diameter, but can become as large as 25 mm. Interestingly, these lesions exhibit rapid growth for the first 2 to 6 weeks. They then enter a stationary phase for another 2 to 6 weeks. Finally, they enter a stage in which they spontaneously involute and form an atrophic, depressed scar. 

The length of each of these stages can be quite variable, and an estimated 5% of keratoacanthomas do recur.2There are also documented cases of deeper invasion. Therefore, keratoacanthomas are routinely treated as squamous cell carcinoma and are excised.1,2

Keratoacanthomas are thought to be strongly associated with sun-exposed areas such as the head, neck, and extremities, with or without pain or tenderness. Elderly fair-skinned individuals are most likely to develop these lesions. 

Dorsal hands in men and lower legs in women are the most common sites. Often, subungual keratoacanthomas do not regress spontaneously and can cause early underlying bone destruction.1,2

Diagnosis can often be made based on clinical presentation, but it is reasonable to perform an excisional biopsy to obtain a histologic diagnosis for confirmation. On histopathology, the lesion will appear quite similar to a low-grade squamous cell carcinoma. 

The crateriform lesion contains an eosinophilic keratin core flanked by acanthotic epithelium. The keratinocytes in the epidermis frequently have a pink, glassy cytoplasm with often a dense inflammatory infiltrate.

Keratoacanthomas characteristically show terminal differentiation where peripheral edges of the tumor lose their infiltrative features, leaving a thin rim of keratinizing cells.2

Differential diagnoses include invasive, more aggressive squamous cell carcinoma; verrucous carcinoma; cutaneous horn; prurigo nodularis; merkel cell carcinoma; and metastatic carcinoma of the skin. 

These lesions typically do not exhibit the triphasic history as seen in keratoacanthomas. However, all these diagnoses can present clinically and morphologically similar to a keratoacanthoma, and therefore all suspicious lesions should be biopsied for a definitive diagnosis. 

Multiple keratoacanthomas or sudden eruption of keratoacanthomas represents cause for concern about the possible presence of such conditions as Muir-Torr Syndrome, keratoacanthoma centrifugum marginatum, Ferguson Smith type multiple self-healing keratoacanthomas, or generalized eruptive keratoacanthomas (Grzybowski variant).1,2

Although keratoacanthomas resolve spontaneously, it is difficult to predict how long this would take. These lesions can also cause destruction of surrounding tissue for up to a year. Therefore, it is generally accepted that these lesions be removed surgically. 

If there are concerns regarding loss of function or cosmetically sensitive areas, nonsurgical treatment can also be considered—for example, intralesional therapies such as 5-fluorouracil solution, bleomycin, or methotrexate. Low-dose methotrexate has also been offered if multiple lesions are present. Radiation therapy may also be used in cases of giant keratoacanthoma if surgical excision is not feasible.2

This patient was treated with excisional biopsy followed by primary intention closure. The specimen was sent to pathology to ensure that the margins were clear. It is important to exclude the diagnosis of a more aggressive squamous cell carcinoma. 


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



HOW TO TAKE THE POST-TEST: This Clinical Advisor CME activity consists of 4 articles. To obtain credit, you must also read Scaly plaques after 
onychomycosis therapy,
 Annular eruption on the lower leg
 and Enduring eruption of papules on the chest. Then take the post-test here.


References 


  1. Bolognia JL, Jorizzo JL, Schaffer JV, eds. Dermatology. 3rd ed. Philadelphia, Pa.: Saunders Elsevier; 2012:1771, 1781-1784.
  2. James WD, Berger TG, Elston DM. Andrews’ Diseases of the Skin: Clinical Dermatology. 11th ed. Philadelphia, Pa.: Saunders Elsevier; 2011:631-633
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