Cutaneous pseudolymphomas: inflammatory reactive proliferations

Skin is an organ of the immune and lymphoid systems. Lymphoid tissue analogous to gut mucosa-associated lymphoid tissue proliferates in the skin in response to antigenic stimulation. This putative skin-associated tissue is called skin-associated lymphoid tissues (SALT). In the opinion of this author, cutaneous pseudolymphomas represent inflammatory, reactive proliferations of SALT following antigenic stimulation of the cutaneous immune cells. Cutaneous pseudolymphomas commonly involve the exposed areas such as head and neck region and upper extremities. They appear as localized nodules, plaques or noduloplaques. They include B- and T-cell pseudolymphomas. Their histologic patterns include nodular, diffuse, band-like and folliculitis-like morphology. Most pseudolymphomas are idiopathic, but some are secondary to known etiologies (drug intake, arthropod assaults, infectious agents and traumas). Cutaneous pseudolymphomas are usually polyclonal proliferations that regress spontaneously or after treating the underlying etiology. Rare cases harbor clonal lymphoid populations and can progress to low-grade lymphomas. Herein, the author reviews the etiology, clinicopathologic features and diagnosis of the cutaneous pseudolymphomas.