Pseudolymphomatous folliculitis: a study of the clinicopathologic and immunohistochemical characteristics of 19 cases and their diagnostic differential

Background: Pseudolymphomatous folliculitis (PLF) is a rare benign cutaneous lymphoid hyperplasia that most commonly occurs in the facial region as a dome-shaped or flat elevated nodule.

Methods: We studied the clinicopathologic and immunohistochemical characteristics of 19 cases of PLF.

Results: The patients comprised 11 females and eight men (mean age 44.9; age range 9-77 years). All cases were solitary except one case with multiple lesions. The lesions were located in the facial region except one that was located in the back. Histologically, there was a diffuse or nodular lymphoid infiltrate with hyperplastic and distorted hair follicles and occasionally enlarged eccrine units with a clear nuclear morphology. Immunohistologically, three cases showed predominantly B-cells, eight cases predominantly B-cells with numerous T-cells, six cases predominantly T-cells with numerous B-cells, and two cases predominantly T-cells. All lesions showed increased numbers of perifollicular dendritic cells expressing anti-S-100 protein and CD1a.

Conclusions: PLF is a rare, benign, cutaneous lymphoid hyperplasia that may resemble cutaneous lymphoma. It has characteristic clinical and pathologic features showing abundant periadnexal S-100/CD1a -positive dendritic cells with dilated and activated pilosebaceous units. The lesion may resolve with complete excision or present spontaneous regression.