RESUMO
Background: Leprosy remains an important health problem mainly in the African and South-East Asia regions. Type 1 reaction is an immune-mediated phenomenon known to complicate at least 30% of patients of leprosy. Diagnosing type 1 reaction correctly is important for timely institution of therapy to prevent and treat neuropathy-associated disability and morbidity. There is paucity of literature on definitive criteria for histologic diagnosis of type 1 reaction. This study was conducted to determine the key histologic variables for diagnosing type 1 reaction. Methods: This was a prospective study recruiting 104 patients with borderline leprosy. Three pathologists blinded to the clinical diagnosis independently assessed the cases. The agreement between each histological variable and clinical diagnosis was then calculated by using Cohen's kappa (Κ) coefficient. Results: Histological diagnosis of type 1 reaction was given to 27 (67.5%) of 40 clinically diagnosed cases of type 1reaction cases. Histological variables chosen as key variables for histological diagnosis of type 1 reaction were presence of giant cells, dermal edema, intragranuloma edema, granuloma fraction 31-50%, and presence of medium to large giant cells. Conclusion: This study has shown that T1R are still underdiagnosed histologically in comparison with clinical assessments. The key variables for diagnosing type 1 reaction were proposed