BackgroundFamilial Mediterranean fever (FMF) is a rare hereditary autoinflammatory disease with disease onset in childhood in most cases. Although autoinflammatory disease awareness is increasing among physicians, delayed diagnosis is still prevalent as a cause of greater morbidity[1].ObjectivesWe aimed to study the characteristics of FMF patients diagnosed between 2000-2010 and 2011-2021 and to see if there was a difference in diagnostic delay.MethodsWe retrospectively evaluated the medical records of the FMF patients followed up in our rheumatology clinic that were diagnosed between 2000-2021 and split them into two groups according to the year they received their diagnosis. There were 1151 patients diagnosed between 2000-2010 (Group 1) and 821 patients diagnosed between 2011-2021 (Group 2). The data studied included gender, age of onset, diagnostic delay, attack characteristics, MEFV mutation, and family history.ResultsThe median current age of patients in Group 1 is 37 years (IQR:30-46) and the median current age of the patients in Group 2 is 36 years (IQR:29-44). The female to male ratio was 1.57 in Group 1 and 1.75 in Group 2, with no significant difference between the groups. Group 2 had later disease onset (p<0.001) and later diagnosis (p<0.001) than Group 1 as shown in the Table 1. The proportion of patients with at least one M694V mutation was higher in Group 2 (p<0.001). The attack durations did not vary between the groups. There was no significant difference in the prevalence of abdominal pain, fever, arthritis, and arthralgia between Group 1 and Group 2. Chest pain (p=0.005), myalgia (p<0.001), and erysipelas-like erythema (p=0.041) were more common in Group 2 than Group 1. Patients with positive family history were more frequent in Group 2 than Group 1 (p=0.046).Table 1.Group 1 (2000-2010, n=1151)Group 2 (2011-2021, n=821)pFemale/Male, n704/447522/2990.275Age at onset, median (IQR) years13 (7-21)18 (12-26)<0.001Delay in diagnosis, median (IQR) years4 (1-11)5,5(2-15)<0.001Attack duration, median (IQR) years3(2-4)3(2-4)0.325Presence of at least one M694V mutation (%)526(46%)390(60%)<0.001Presence of abdominal pain in the initial attack (%)936(81%)669(81%)0.926Presence of fever in the initial attack (%)855(74%)592(72%)0.281Presence of chest pain in the initial attack (%)218(19%)199(24%)0.005Presence of arthritis in the initial attack (%)330(29%)215(26%)0.224Presence of arthralgia in the initial attack (%)213(19%)170(21%)0.223Presence of myalgia in the initial attack (%)45(4%)65(8%)<0.001Presence of erysipelas like erythema in the initial attack (%)31(3%)36(4%)0.041Presence of positive family history (%)652(57%)502(61%)0.046ConclusionThere was some increase in the diagnostic delay in 2011-2021 compared to 2000-2010. This may be partly due to the later onset of symptoms in patients diagnosed in 2011-2021, which could have led the physicians to consider other differential diagnoses. Nevertheless, diagnostic delay in FMF still seems a prevalent problem that should be addressed to prevent excess morbidity and mortality.References[1]Erdogan M, Ugurlu S, Ozdogan H, Seyahi E. Familial Mediterranean fever: misdiagnosis and diagnostic delay in Turkey. Clin Exp Rheumatol. 2019;37 Suppl 121(6):119-124.Disclosure of InterestsNone declared