Diagnostic Challenges and Therapeutic Considerations in Adult-Onset Still's Disease: A Clinical Case Report.

Adult-onset Still's disease (AOSD) is an uncommon systemic inflammatory disorder that presents with diverse, overlapping symptoms, complicating the diagnostic process due to its nonspecific clinical features and the absence of a definitive diagnostic test. Diagnosis is often challenging and relies on excluding other conditions while maintaining a high index of suspicion, supported by specific diagnostic criteria such as Yamaguchi or Fautrel. Prompt recognition and a multidisciplinary approach are essential, as AOSD can progress to life-threatening multiorgan dysfunction due to a hyperinflammatory response. We report the case of a 58-year-old male car mechanic with no prior medical history who presented with a three-month history of persistent fever, bilateral hip pain, and systemic symptoms. On examination, he was febrile (39.4°C) with tachycardia, tachypnea, and elevated inflammatory markers with eosinophilia. Despite a comprehensive workup, including imaging and broad-spectrum antibiotics, his condition progressed, marked by the emergence of a characteristic salmon-pink rash, altered mental status, and persistent fever. Significant findings included markedly elevated ferritin levels (43,980 ng/mL), normal creatine kinase, negative autoimmune markers, and PET-CT revealing fluorodeoxyglucose (FDG)-avid intramuscular sites. A muscle biopsy demonstrated perivascular lymphocytic infiltration. A diagnosis of AOSD was established, and high-dose corticosteroids were initiated, leading to initial improvement. However, the patient developed complications, including acute kidney injury, steroid-induced diabetes, resistant hypertension, and cardiopulmonary symptoms, eventually succumbing to acute respiratory failure six weeks post-discharge. This case underscores the severe potential trajectory of AOSD and the complex diagnostic and therapeutic challenges associated with its management.