**Core Concept**
Reflex Sympathetic Dystrophy (RSD), now known as Complex Regional Pain Syndrome Type 1 (CRPS-1), is a chronic pain condition characterized by intense burning pain, swelling, and sensitivity in one of the limbs following an injury. This condition involves a sympathetic nervous system response, leading to vasomotor and sudomotor dysfunction.

**Why the Correct Answer is Right**
The pathophysiology of RSD/CRPS-1 involves an abnormal sympathetic nervous system response to an injury, leading to excessive release of neurotransmitters such as substance P and calcitonin gene-related peptide (CGRP). This results in vasodilation, increased blood flow, and edema. The sympathetic nervous system also contributes to the development of pain through the release of pain-producing substances. The condition is further complicated by the involvement of the immune system and the release of inflammatory mediators.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not mention the underlying sympathetic nervous system dysfunction that is key to the pathophysiology of RSD/CRPS-1.
**Option B:** This option is incorrect because it only mentions pain as a symptom of RSD/CRPS-1 without addressing the underlying pathophysiological mechanisms.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of RSD/CRPS-1 is allodynia, which is pain caused by a stimulus that does not normally cause pain, such as light touch or temperature changes. This is an important diagnostic clue and can help differentiate RSD/CRPS-1 from other pain conditions.

**Correct Answer: C. RSD/CRPS-1 is characterized by sympathetic nervous system dysfunction leading to vasomotor and sudomotor dysfunction.**