Systemic lupus erythematosus (SLE) is an autoimmune-mediated connective tissue disorder primarily diagnosed in women between the ages of 20 and 40. SLE can affect various parts of the body, including the skin, joints, kidneys and brain. Pain is considered as an early symptom of autoimmune diseases and characterizes the so-called predisease phase in SLE. Fibromyalgia syndrome (FMS) is a comorbid condition diagnosed in approximately 30% of SLE patients. FMS is characterized by widespread pain and tenderness in the muscles, entheses, and tendons without inflammatory signs observable through imaging techniques. This pain is often accompanied by additional symptoms such as sleep disturbances, fatigue, memory issues, and depression.One significant issue is the lack of systematic screening for FMS in SLE patients, leading to frequent underdiagnosis. Late diagnosis is a major problem, as it allows the condition to progress, making early detection essential to improve outcomes in autoimmune diseases like SLE.This project aims to characterize SLE patients with FMS, investigating whether behavioral measurements (e.g. physical activity) can indicate the presence or activity of FMS. Additionally, we will compare objective assessments of FMS severity with patients' subjective experiences.To achieve these goals, I will identify FMS patients within an SLE cohort using the 2016 ACR criteria for fibromyalgia. Patients will wear sensors to monitor physical activity, and an app will be used to assess pain levels and capture patients' subjective evaluations of their physical activity.