In Still’s disease the transient cutaneous rash coinside with the fever spike. The rash is due to:
**Core Concept**
Still's disease, also known as juvenile rheumatoid arthritis, is a rare autoimmune disorder characterized by chronic inflammation and fever. The transient cutaneous rash, known as salmon patch or erythema, is a hallmark symptom that coincides with fever spikes.
**Why the Correct Answer is Right**
The rash in Still's disease is due to the deposition of immune complexes in the skin, leading to activation of the complement system and subsequent inflammation. This process is mediated by the release of cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha), which are produced in response to the inflammatory stimulus. The activation of the complement system and the release of cytokines result in the characteristic salmon-colored rash.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the rash in Still's disease is not caused by a direct allergic reaction to an allergen. While allergic reactions can cause skin manifestations, the pathophysiology of Still's disease is distinct.
**Option B:** This option is incorrect because the rash in Still's disease is not due to a bacterial or viral infection. While infections can cause skin rashes, the rash in Still's disease is a result of the autoimmune response.
**Option C:** This option is incorrect because the rash in Still's disease is not caused by a vasculitic process. While vasculitis can cause skin manifestations, the rash in Still's disease is a result of immune complex deposition and complement activation.
**Clinical Pearl / High-Yield Fact**
The rash in Still's disease is often described as a "salmon-colored" patch and is typically accompanied by a high fever. This classic combination should raise suspicion for Still's disease in children with chronic arthritis.
**Correct Answer: C. Deposition of immune complexes in the skin.**