**Core Concept**
Polymyalgia rheumatica (PMR) is a chronic inflammatory disorder characterized by proximal muscle pain and stiffness, predominantly in individuals over 50 years old. The Healey criteria are used for the diagnosis of PMR, which includes a combination of clinical and laboratory features.

**Why the Correct Answer is Right**
The Healey criteria for PMR include:
- Age over 50 years
- Proximal muscle pain and stiffness
- ESR of 40 mm/h or higher
- Morning stiffness lasting more than an hour
- Improvement with glucocorticoids

The correct answer will not meet one of these criteria, indicating a feature not included in the Healey criteria.

**Why Each Wrong Option is Incorrect**
**Option A:** Age over 50 years
* This is one of the inclusion criteria for PMR, so it is not the correct answer.

**Option B:** Proximal muscle pain and stiffness
* This is also one of the inclusion criteria for PMR, so it is not the correct answer.

**Option C:** Elevated creatine kinase (CK) levels
* Elevated CK levels can be seen in various muscle disorders and are not a specific criterion for PMR.

**Option D:** Improvement with NSAIDs
* While NSAIDs may provide some relief from symptoms, the Healey criteria specifically mention improvement with glucocorticoids, not NSAIDs.

**Clinical Pearl / High-Yield Fact**
It is essential to note that PMR is often associated with giant cell arteritis (GCA), and patients with PMR should be screened for GCA, especially if they present with visual symptoms or new-onset jaw claudication.

**Correct Answer: C. Elevated creatine kinase (CK) levels**