**Core Concept**
Somatoform disorders are characterized by the presence of physical symptoms that have no clear medical explanation, and are often associated with significant distress or impairment in social, occupational, or other areas of functioning. These disorders are distinct from factitious disorders, where individuals intentionally produce or feign symptoms.

**Why the Correct Answer is Right**
Fibromyalgia is a chronic condition characterized by widespread musculoskeletal pain, fatigue, and tender points, but it is not classified as a somatoform disorder. This is because fibromyalgia is believed to be a distinct neurobiological disorder, involving central sensitization and abnormalities in pain processing, rather than a psychological or psychiatric condition. The exact pathophysiology of fibromyalgia is not fully understood, but it is thought to involve a complex interplay between genetic, environmental, and hormonal factors.

**Why Each Wrong Option is Incorrect**
**Option A:** Somatization disorder is a classic example of a somatoform disorder, characterized by multiple, recurring physical complaints that are not explained by a medical condition, substance use, or another mental disorder. It is a specific somatoform disorder.
**Option C:** Chronic fatigue syndrome, also known as myalgic encephalomyelitis, is a condition characterized by persistent and profound fatigue that is not alleviated by rest. It is often associated with somatic symptoms and is considered a somatoform disorder.
**Option D:** Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by recurrent abdominal pain and changes in bowel habits, without any clear medical explanation. It is often classified as a somatoform disorder.

**Clinical Pearl / High-Yield Fact**
When evaluating patients with somatoform disorders, it's essential to remember that these conditions often involve a complex interplay between psychological, social, and biological factors. A thorough diagnostic evaluation should include a comprehensive medical history, physical examination, and psychological assessment to rule out underlying medical conditions and identify potential contributing factors.

**✓ Correct Answer: B. Fibromyalgia**