RESUMEN
BACKGROUND: Lymphocytic infiltration of the skin (LIS) and reticular erythematous mucinosis (REM) are characterized histologically by an inflammatory cutaneous lymphocytic infiltrate similar to the histological appearance of pseudolymphoma. OBJECTIVES: To re-evaluate a large cohort of patients with the clinical and/or histological diagnosis or differential diagnosis of LIS and REM and to assess the evidence for infection with Borrelia. METHODS: Sixty-nine cases of LIS and 34 cases of REM were retrospectively investigated. Haematoxylin and eosin sections were re-examined, and histological diagnoses were specified and confirmed by clinicopathological correlation. Evidence for Borrelia infection was assessed by immunohistochemistry and focus-floating microscopy (FFM). RESULTS: LIS appeared to serve as a collective term for two main clinicopathological reaction patterns: (i) (tumid) lupus erythematosus (LE) (32 of 69, 46%) and (ii) pseudolymphoma (31 of 69, 45%). Other diagnoses (five of 69, 7%) included polymorphic light eruption, arthropod bite reaction, spongiotic dermatitis, drug eruption and urticaria. Spirochaetes were detected by FFM in 24 of 31 (77%) cases with a pseudolymphomatous reaction, while all nonpseudolymphomatous reactions were negative. Of the cases initially considered as REM, 21 of 34 (62%) were classified as LE, four of 34 (12%) as pseudolymphoma (three of four positive for Borrelia), and five of 34 (15%) as other diagnoses (folliculitis, morphoea, seborrhoeic dermatitis, prurigo and arthropod bite reaction). The diagnosis of Borrelia-associated pseudolymphoma was made significantly more often in those cases where LIS was considered as initial differential diagnosis than REM (P < 0.05). CONCLUSIONS: LIS and REM seem to represent clinicopathological reaction patterns. Our results confirm that, after accurate clinicopathological correlation, most cases of both conditions constitute hidden variants of LE. Furthermore, LIS, in contrast to REM, frequently comprises pseudolymphomatous reactions including borrelial lymphocytoma.