Upgrading type1 lepra reaction or reversal reaction (RR) is an acute inflammatory complication of leprosy and a disparity exists between clinicians and pathologists for diagnosing a RR. Inter-observer variations among pathologists also compound this problem as no universally agreed diagnostic criteria exist. 120 biopsies and H&E stained slides were assessed by 3 pathologists. The pathologists were blinded to the clinical diagnosis and to each other's observations. Each pathologist assigned a likelihood of reaction by their histopathological observations as definitely reaction, probable reaction and no reaction. Clinicopathological correlation and interobserver agreement was analyzed statistically. Discordance between clinical and histopathological diagnosis was seen in 30.8% by pathologist 1(P1), 23.7% by pathologist 2 (P2) and 34.5% by the pathologist 3 (P3). Dermal edema, intragranuloma edema and epidermal erosion were consistent findings by all observers. Definite reaction was seen in 54.2% of cases by P1, 53.3% by P2 and 34.5% by P3. Kappa statistics for strength of agreement showed good agreement between 3 pathologists with P1 (ê=0.83), P2 (ê= 0.61), P3 (ê=0.62). RR are underdiagnosed on histopathological examination but this study shows that dermal edema, edema within the granuloma and partial obliteration of grenz zone by granuloma are reliable clues to diagnose a RR on histopathology. Key words: Leprosy, Reversal Reaction, Type 1 Reaction http://www.ijl.org.in Short Communication Received : 26.05.2014 Revised : 20.06.2015 Accepted : 23.06.2015 Indian J Lepr 2015, 87 : 101-107 © Hind Kusht Nivaran Sangh, New Delhi 1 2 M Kaur, MBBS, MD, Pathology, Sr Resident, National Institute of Pathology (ICMR), New Delhi 3 AK Mishra, National Institute of Pathology (ICMR), New Delhi 4 N Sood, Departments of Pathology, DDU Hospital, New Delhi 5 V Ramesh, Department of Dermatology, Venereology and Leprology, Safdarjung Hospital, New Delhi 6 A Kubba, Delhi Dermpath Laboratory, New Delhi 7 A Singh, MBBS, MD, Scientist-D, National Institute of Pathology (ICMR), New Delhi Correspondence to: Avninder Singh Email: avninders@hotmail.com I Sharma, Research Scholar, National Institute of Pathology (ICMR), New Delhi Histopathological Diagnosis of Leprosy Type 1 Reaction with Emphasis on Interobserver Variation 1 2 3 4 5 6 7 I Sharma , M Kaur , AK Mishra , N Sood , V Ramesh , A Kubba , A Singh Introduction Leprosy remains a health problem in different parts of the world. At the end of first quarter of 2013, 189018 patients were affected by leprosy (prevalence rate 0.32 per 10000 population) as compared to 2012 where it was 181941 (0.34 per 10000) (WHO 2013). Leprosy type 1 reaction also called as upgrading reversal reaction (RR) is a delayed type hypersensi- tivity reaction in borderline forms of leprosy spectrum and is characterized by increased cell mediated immunity with influx of CD4+ T cells