pseudolymphomatous folliculitis ( plf ) is a rare lesion of which few reported cases exist . the clinical appearance is characterized by solitary or multiple large , firm violaceous nodules that occur mainly on the face , scalp , and upper trunk 1 . typically , rapid growth is seen over a period of several weeks or months 1 , making distinguishing plf from malignant lymphoma clinically difficult . we treated a case of subcutaneous plf on the left cheek and herein present the characteristic pathological findings . a 51yearold male visited our hospital with multiple rapidly enlarging masses in the left cheek that had been developing for 1 month . he had a history of cerebral infarction , and clopidogrel sulfate had been administered to prevent another infarction . physical examination revealed three firm , red , domeshaped subcutaneous nodules on the left cheek , two of which were located between the ear and the jaw , with the remaining one near the nose . the three nodules measured 7  10 , 6  5 , and 5  5 mm , respectively . 1a ) . based on our suspicion of inflamed epidermal cysts , surgical excision of the two lesions between the ear and the jaw was performed under local anesthesia 1 month after the initial examination . with consideration of the influence of inflammation , those two tumors were removed along with fat in the immediate area surrounding the tumors . we did not remove all three tumors at the same time because of the risk of hemorrhage due to the anticoagulant medication . after confirming that postsurgical bleeding was controlled , the remaining tumor , located near the nose , was removed 12 days after the first operation , under local anesthesia ( fig . preoperative view of the tumor near the nose , taken 12 days after the first excisional biopsy for the other two tumors ( as indicated by the arrow ) , showing slight regression after the first visit ( b ) . pathological findings of the tumors excised at the first operation showed a nodular dense lymphoid cell infiltration from the dermis to the subcutaneous tissue . the cells had been enlarged and the hair follicles had been destroyed by infiltration of the dense , diffuse , and small welldifferentiated lymphocytes ( fig . , immunohistochemical examination revealed that a large number of lymphocytic cells were positive for cd3 , s100 , and cd1a ( fig . 2d , f and g ) , while few were positive for cd20 and few were positive for pd1 ( fig . enlarged and distorted hair follicles are surrounded by a dense diffuse infiltration of cells ( a , b ) . the infiltrating cells were mainly composed of small lymphocytes with some blast celllike large cells ( c ) . immunostaining revealed sheets of cd3 + t lymphocytes ( d ) and scattered cd20 + b lymphocytes ( e ) . furthermore , a large number of lymphocytic cells were positive for s100 and cd1a ( fig . 2f and g ) , whereas few lymphocytic cells were positive for pd1 ( fig . ( magnification : a , 2 ; b , 10 ; c , 40 ; dh , 10 ) . however , in a pathological examination of the excised whole tumor at the second operation , mild lymphocyte infiltration around the hair follicles was found , which was not considered to be a plfspecific finding ( fig . taking all findings into account , the patient was diagnosed as having mild or regressed plf . six months after the second operation , healing progressed and no recurrence was noted ( fig . plf is characterized by a dense lymphoid infiltration accompanied by hyperplastic hair follicles , and was first described as a distinct variant of pseudolymphoma in 1986 3 . thereafter , only approximately 10 reports on plf , including 76 cases , have been published ; thus , it is considered to be a rare entity . according to those past reports , typical plf is presented as a solitary , erythematous or violaceous , domeshaped or flat elevated nodule on the face , especially on the nose , cheek , eyelid , or forehead 4 , 5 . in many cases , the eruption is isolated 5 , whereas our patient showed a relatively rare pattern of eruption , as the plf manifested as multiple lesions . plf occurs in a wide age range and both sexes 5 ; however , its tendency is yet to be elucidated because of the low number of reports . to the best of our knowledge , no cases of spontaneous regression without any treatment ( operation , biopsy , medication , etc . ) have been reported . a variety of differential diagnoses , including epidermal cyst , chronic folliculitis , granuloma , basal cell carcinoma , sarcoidosis , and insect bite reaction must be considered 1 , 5 , with malignant lymphoma being one of the most important . thus , careful histological and immunohistochemical examinations are needed for accurate diagnosis of plf 1 . 4 proposed histological criteria for diagnosis , including nodular dense lymphocytic infiltration from the dermis to subcutis , befitting the term pseudolymphoma , in which lymphocytes surround and infiltrate the pilosebaceous unit , and deform the walls . 5 presented 42 cases of plf in which hair follicles were enlarged and often distorted , with a dense diffuse lymphoid infiltration composed mainly of small welldifferentiated lymphocytes , occupying the whole dermis , though sparing of the epidermis was also observed . immunohistologically , plf can be divided into four groups : predominance of b cells , predominance of b cells with fairly numerous t cells , predominance of t cells with fairly numerous b cells , and predominance of t cells 4 . recently , goyal et al . 2 reported that pd1 + t cells and cd1a are useful for differentiation of plf . in our case , c ) , as well as sheets of cd3 + t lymphocytes and scattered cd20 + b lymphocytes ( fig . 2d and e ) . furthermore , a large number of lymphocytic cells were positive for s100 and cd1a ( fig . 2f and g ) , whereas few lymphocytic cells were positive for pd1 ( fig . in contrast to lymphomas , lymphocytes in plf show no bias with regard to their /chainpositive bcell ratio or cd4+/8 + tcell ratio . in addition , the results of polymerase chain reaction assays for clonal tcell receptor and immunoglobulin heavy chain gene rearrangements typically reveal negative findings in plf cases 6 . since we already had a diagnosis , we did not perform additional immunohistological examination . on the other hand , in the specimen obtained in the second operation , we found only mild lymphocyte infiltration around the hair follicles and common findings of inflammation ; therefore , a diagnosis of plf could not be made from that evidence alone . the first choice of treatment for plf is excisional biopsy , with the use of corticosteroid injections recommended if the excision is not complete 1 . in cases with multiple lesions , such a biopsy should be performed on one lesion , and once plf is determined , monitoring of any remaining tumors is considered to be the best treatment . there are a few reports of plf nodules regressing spontaneously within 6 months after excisional biopsy 7 , 8 . in cases of plf diagnosed by partial biopsy , it is recommended to followup for half a year , and wait for spontaneous improvement . careful examination of patients with plf is required because distinguishing plf from malignant lymphoma is difficult . in such cases , an excisional biopsy is the most useful method for making an accurate diagnosis . in consideration of the difficulty of diagnosis , an excisional biopsy is valuable ; however , once plf is diagnosed in one of the multiple tumors by excisional biopsy , such a biopsy is thought to be unnecessary for the remaining tumors .
key clinical messagepseudolymphomatous folliculitis ( plf ) is a rare lesion . 
 sometimes , the clinical appearance is characterized by multiple large , firm violaceous nodules . in cases with multiple lesions , 
 such biopsy should be performed on one lesion , and once plf is determined , monitoring for the remained tumor is considered to be the best treatment .