Pityriasis lichenoides--an immune complex disease.

Circulating immune complexes have been detected in patients with pityriasis lichenoides during disease activity when IgM and C3 have been observed in dermal vessels on direct immunofluorescence of fresh lesions. This implies that pityriasis lichenoides is an immune complex disorder and that deposited complexes play a part in the pathogenesis of the condition. There is a characteristic pattern of immunofluorescence which may be a diagnostic aid.