What are typical histopathological findings?
Histopathological findings vary with the stage of the disease, are often not diagnostic and may resemble other chronic skin diseases. As sun-damaged skin is mostly prominent in rosacea patients, severe elastosis is a constant feature. The papules in rosacea may have a granulomatous appearance, which can mimic sarcoidosis or lupus vulgaris.
In the early stages of rosacea the main features are slight edema, ectatic venules and a mild nonspecific perivascular lymphocytic infiltrate in the dermis. A slight hyperplasia of the elastic tissue is associated and elastolysis may be present (increased curled, thickened elastic fibers).
Later lesions show an advance of the perivascular and perifollicular infiltration of the dermis, consisting of lymphocytes and histiocytes with a variable number of plasma cells and giant cells. Acute folliculitis with follicular and perifollicular pustules and destruction of the hair follicle may be seen. The vessels are thickened and grossly dilated. Elastosis is increased.
Stage III of rosacea is characterized by a diffuse expansion of the connective tissue. The sebaceous glands are increased and the follicular canals are dilated and contain keratinous debris. Epithelialized tunnels undermine the hyperplastic tissue. Demodex folliculorum mites may be seen to densely populate the pilosebaceous follicles.