Blueberry muffin baby is a term used to describe the characteristic distributed purpura

Purpura

Purpura is the appearance of red or purple discolorations on the skin that do not blanch on applying pressure. They are caused by bleeding underneath the skin...

 due to extramedullary hematopoiesis

Extramedullary hematopoiesis

Extramedullary hematopoiesis refers to hematopoiesis occurring outside of the medulla of the bone.In some cases, it may be physiologic. For example, during fetal development, hematopoiesis occurs at many different locations, such as the liver and spleen....

 found in infants.

It was originally considered characteristic of rubella

Rubella

Rubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...

, but is now considered to be potentially associated with many other conditions, such as cytomegalovirus

Cytomegalovirus

Cytomegalovirus is a viral genus of the viral group known as Herpesviridae or herpesviruses. It is typically abbreviated as CMV: The species that infects humans is commonly known as human CMV or human herpesvirus-5 , and is the most studied of all cytomegaloviruses...

 and metastatic neuroblastoma

Neuroblastoma

Neuroblastoma is the most common extracranial solid cancer in childhood and the most common cancer in infancy, with an annual incidence of about 650 cases per year in the US , and 100 cases per year in the UK . Close to 50 percent of neuroblastoma cases occur in children younger than two years old...

.

It derives its name from the superficial similarity to a blueberry

Blueberry

Blueberries are flowering plants of the genus Vaccinium with dark-blue berries and are perennial...

 muffin

Muffin

A muffin is an American English name for a type of quick bread that is baked in small portions. Many forms are somewhat like small cakes or cupcakes in shape, although they usually are not as sweet as cupcakes and generally lack frosting. Savory varieties, such as cornbread muffins, also exist...

.