Objective: To analyze clinicopathological features of parapsoriasis. Methods: Clinical and pathological data were collected from 81 patients with parapsoriasis in Department of Dermatology, Peking University First Hospital between January 2016 and May 2018, and analyzed retrospectively. Results: Among the 81 patients with parapsoriasis, 44 were male and 37 were female, with age ranging from 6 to 77 years. Their disease course ranged from 7 days to 30 years, and the median disease course was 12 months. Moreover, 61 (75.3%) patients were aged less than 40 years, and 20 (24.7%) were aged 41 years and older. Of the 81 patients, 16 (19.8%) were diagnosed with small plaque parapsoriasis, 20 (24.7%) with large plaque parapsoriasis, 37 (45.7%) with pityriasis lichenoides chronica, and 8 (9.9%) with pityriasis lichenoides et varioliformis acuta. Additionally, distribution patterns of lesions included diffuse type in 65 cases (80.2%) , central type in 6 cases (7.4%) , and peripheral type in 10 cases (12.3%) . Histopathological examination of skin lesions revealed liquefaction degeneration of basal cells in 69 cases (85.2%) , migration of lymphocytes into the epidermis in 67 cases (82.7%) , focal parakeratosis in 42 cases (51.9%) , keratinocyte necrosis in 29 cases (35.8%) , extravasation of erythrocytes in 23 cases (28.4%) , epidermal spongiosis in 21 cases (25.9%) , and dermal perivascular focal infiltration in 61 cases (75.3%) . Conclusion Parapsoriasis has characteristic clinical and pathological manifestations, and a close combination of clinical manifestations with pathological features is necessary for its accurate diagnosis.

A 44-year-old male patient presented with a subcutaneous nodule in the left little finger for 3 years. Skin examination showed a subcutaneous nodule with rubber-like hardness but no tenderness on palpation, measuring 0.4 cm × 0.4 cm in size at the dorsal distal aspect of the left little finger, and the movement of the distal interphalangeal joint was unrestricted. Postoperative histopathological examination revealed that the tumor contained abundant stroma consisting of variable fiberous, chondroid and myxoid materials; tumor cells were oval to short spindle-shaped with inconspicuous nucleoli but no mitosis; cells were arranged haphazardly or in small clusters. Immunohistochemical study showed positive staining for vimentin, CD34 and transcription factors ERG and SOX9, but negative staining for S100, P63, broad-spectrum cytokeratin AE1/AE3, epithelial membrane antigen, smooth muscle actin and desmin in tumor cells, and the Ki67 labeling index was below 1%. Finally, the patient was diagnosed with acral fibrochondromyxoid tumor.