A client is diagnosed with obsessive-compulsive disorder (OCD). Which symptom pattern is MOST characteristic?

OCD (Obsessive-Compulsive Disorder) is defined by two core features: OBSESSIONS — persistent, intrusive, unwanted thoughts, urges, or images that cause marked anxiety or distress; common themes: contamination (fear of germs), harm (fear of hurting others accidentally), symmetry (things must be 'just right'), forbidden thoughts; the person recognizes the thoughts as excessive or irrational (INSIGHT — distinguishes OCD from psychotic disorders); COMPULSIONS — repetitive behaviors or mental acts the person feels driven to perform in response to the obsession; temporary anxiety relief is the reinforcer that maintains the cycle; behaviors: handwashing, checking, counting, ordering/arranging, repeating; mental acts: praying, counting mentally, replacing a bad thought with a 'good' one; CYCLE: Obsessive thought → anxiety → compulsion → temporary relief → obsession returns → cycle repeats. IMPAIRMENT: OCD must cause significant distress or functional impairment; mild orderliness or preferences for cleanliness are NOT OCD; OCD symptoms are egodystonic (the person finds them distressing and unwanted, unlike obsessive-compulsive PERSONALITY traits which are ego-syntonic). TREATMENT: Cognitive-behavioral therapy with ERP (Exposure and Response Prevention) is the gold standard; SSRIs (fluoxetine, fluvoxamine, sertraline, paroxetine) are first-line medication; combination of CBT+SSRI is most effective.