EPP

Diagnosis

The disease is diagnosed in patients with light sensitivity by testing blood and stool for the presence of abnormally high levels of protoporphyrin. Contrary to what is found in the other porphyrias, urine porphyrin levels remain within normal limits in EPP. When a smear of blood from a patient is examined under the fluorescence microscope, large numbers of red fluorescing erythrocytes are seen; these are not seen in persons who do not have this disorder.

In addition, if the skin of the light-exposed areas of the body is examined under the light microscope, an amorphous homogeneous substance in and around the walls of small blood vessels of the upper papillary dermis will be seen. Histologic studies suggest that this substance is a neutral mucopalysaccharide, glycoprotein or mucoprotein. EPP is genetically transmitted as an autosomal dominant trait with variable penetrance and expressivity. Some relatives of patients may also have only slightly elevated levels of protoporphyrin but are asymptomatic, suggesting the existence of a carrier state.