Hematological and Inflammatory Markers in Isotretinoin-Associated Sacroiliitis: A Prospective Cohort Study

Introduction: Low back pain (LBP) and sacroiliitis have been reported during isotretinoin therapy, but the role of inflammatory markers in identifying sacroiliitis remains unclear. Objectives: This study aimed to determine the frequency of LBP and sacroiliitis during isotretinoin therapy and investigate whether any hematological or inflammatory parameter could help identify magnetic resonance imaging (MRI)-confirmed sacroiliitis. Methods: This prospective cohort study included 220 patients receiving isotretinoin for moderate-to-severe acne. Patients reporting pain at rest or morning stiffness lasting longer than one hour were referred for MRI. Hematological and inflammatory parameters, including C-reactive protein erythrocyte sedimentation neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), monocyte-to–high-density lipoprotein ratio (MHR), red blood cell distribution width (RDW)-to-lymphocyte and RDW-to-platelet ratio, systemic immune-inflammation index (SII), and systemic inflammatory response index (SIRI) were compared among patients with MRI-confirmed sacroiliitis, MRI-negative inflammatory LBP, and no LBP. Results: LBP occurred in 81 patients (36.8%); 59 (26.8%) met the study-defined inflammatory pain criteria, and 22 (10.0%) had mechanical pain. Six MRI-eligible patients declined imaging. Sacroiliitis was identified in 22 patients, representing 10.0% of the enrolled cohort, 10.3% after excluding MRI refusals. No significant between-group differences were observed in the evaluated hematological or inflammatory parameters (all p>0.05). Conclusions: Isotretinoin-associated sacroiliitis occurs with notable frequency. The evaluated markers did not differ significantly among the groups. Clinical assessment and MRI may be more informative than inflammatory markers in distinguishing isotretinoin-associated sacroiliitis from MRI-negative inflammatory LBP. Further studies are needed to establish their diagnostic utility and investigate alternative biomarkers for identifying isotretinoin-associated sacroiliitis.