S4497 Chronic Functional Bowel Disorder With Fibromyalgia in a 52-Year-Old Man: A Case of Persistent Multisystem Symptoms

Introduction: Functional bowel disorders like irritable bowel syndrome (IBS) are increasingly diagnosed in clinical practice and frequently overlap with somatic syndromes such as fibromyalgia. These coexisting conditions present diagnostic and therapeutic challenges due to their shared mechanisms, including central sensitization and gut-brain axis dysfunction. Recent studies underscore the impact of altered gut microbiota and hypothalamic-pituitary-adrenal (HPA) axis dysregulation in perpetuating systemic symptoms. This case highlights the complexity of managing IBS with fibromyalgia in a middle-aged man, emphasizing the need for a multidisciplinary, integrative treatment approach. Case Description: A 52-year-old man with controlled hypertension presented with 1 year of abdominal bloating, cramping pain relieved by defecation, and alternating diarrhea and constipation. He also reported experiencing postprandial bloating, particularly after consuming fermentable oligo-, di-, mono-saccharides and polyols (FODMAP)-rich meals. Over 6 months, he developed widespread soft-tissue pain affecting the neck, shoulders, back, hips, and thighs, along with morning stiffness, fatigue, cognitive slowing, and non-restorative sleep. Symptoms were stress-sensitive and unrelieved by rest. Lab evaluation, including complete blood count, erythrocyte sedimentation rate, C-reactive protein, thyroid-stimulating hormone, vitamin B12, and colonoscopy, was unremarkable, except for vitamin D deficiency (16 ng/mL). Rheumatologic workup was negative. He met Rome IV criteria for IBS with mixed bowel habits and American College of Rheumatology/European League Against Rheumatism 2010 classification criteria for fibromyalgia. Management began with a low-FODMAP diet and the use of probiotics. Amitriptyline was replaced by duloxetine (30 mg daily) for persistent pain and fatigue. Melatonin and cognitive behavioral therapy were added for sleep and stress management, alongside vitamin D supplementation. At 3 months, the patient reported moderate symptom relief, improved concentration, better sleep, and a reduction in absenteeism. Discussion: IBS and fibromyalgia share overlapping mechanisms, including gut dysbiosis, central sensitization, and immune modulation. Reduced levels of Bifidobacteria and Lactobacilli, along with increases in pro-inflammatory microbes, are common in both. This case supports the role of gut-brain-microbiome dysfunction in multisystem disorders. Multimodal therapy targeting both gastrointestinal and systemic pathways can improve outcomes in complex, comorbid presentations.