Because of the COVID19 pandemic, you are practicing telemedicine. Your patient is a 25-year-old woman whose main complaint is "a skin rash" for the past 3-4 hours (see photo below). The rash is not pruritic or painful and is unassociated with any systemic manifestations. The patient recovered from "mononucleosis" about 4 weeks ago. You are told the exam, including her vital signs, is otherwise perfectly normal. The arrow in her photograph points to a biopsy site.
What is your diagnosis, what test(s) would you order to confirm your suspicions, and what treatment, if any, do you recommend?
DIAGNOSIS: Cold agglutinin syndrome (CAS) presenting as livedo racemosus.
CAS is distinguished from the more common cold agglutinin disease (CAD) in that CAS is secondary to an infectious disease (usually EBV mononucleosis or mycoplasma pneumoniae) or an aggressive lymphoma. In contrast, CAD is a specific B-cell mediated autoimmune hemolytic anemia involving activation of the classical pathway of complement that leads to C3b-mediated erythrophagocytosis. The preferred treatment of CAD is rituximab or rituximab plus fludarabine. In the presented case, erythrocytes agglutinated at an unusually high temperature, causing obstruction to blood flow in her superficial papillary venous plexi (note the typical hexagonal pattern of these plexi). Upon warming her core temperature, the livedo disappeared. Serology confirmed recent infection with EBV, and the livedo resolved within several weeks.