What is the cause for her bump?

An 80-year-old female presents with a persistent red bump on her back of 3 months duration. She is otherwise healthy and has been taking the same statin drug for over 5 years. She said the bump is asymptomatic.

What is the cause for her bump?
A. Persistent tick bite reaction
B. Epidermoid cyst
C. Cutaneous B-cell lymphoma
D. Amelanotic melanoma
E. Irritated seborrheic keratosis

(Answer and discussion on next page)

Answer: Cutaneous B-cell lymphoma

A biopsy confirmed the diagnosis of a cutaneous B-cell lymphoma (CBCLs). Primary CBCLs represent 20% to 25% of all cutaneous lymphomas and tend to have an overall favorable prognosis. The workup includes using histomorphology and cytomorphology, immunohistochemistry and phenotypic features, and genotyping. 

Treatments may include surgical excision, antibiotics, and radiotherapy. Overtreatment should be avoided. 

Differential diagnosis. Tick bite is typically very pruritic. Epidermoid cyst has a cystic feel unlike the nodule seen here. Seborrheic keratoses have a characteristic surface texture that is not seen here. Melanoma can only be excluded by biopsy.