## **Core Concept**
The patient's presentation suggests an acute inflammatory arthritis, specifically pseudogout or calcium pyrophosphate deposition disease (CPPD), given the presence of rhomboid crystals with weak-positive birefringence in the joint fluid. This condition often presents with sudden onset of joint pain, swelling, and warmth, typically affecting larger joints like the knee.

## **Why the Correct Answer is Right**
The presence of rhomboid-shaped crystals with weak-positive birefringence under polarized light microscopy is diagnostic of CPPD disease. The management of acute CPPD involves symptomatic relief and anti-inflammatory measures. Nonsteroidal anti-inflammatory drugs (NSAIDs) are often the first line of treatment for acute CPPD attacks, making option **C. Administer NSAIDs** the most appropriate next step. NSAIDs help reduce inflammation, pain, and swelling.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While educating the patient about the condition is important, it does not address the immediate need for symptomatic relief and management of inflammation.
- **Option B:** Although colchicine can be used for acute gout and sometimes CPPD, it is not the first-line treatment for CPPD disease due to potential gastrointestinal side effects and the availability of more effective treatments like NSAIDs.
- **Option D:** Intra-articular corticosteroids can be considered for CPPD, especially if NSAIDs are contraindicated. However, they are typically considered after NSAIDs have been tried or in specific scenarios, not as the immediate next step.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that CPPD disease can mimic gout but is distinguished by the type of crystals found in the synovial fluid: monosodium urate crystals in gout exhibit strong-negative birefringence, whereas calcium pyrophosphate dihydrate crystals in CPPD exhibit weak-positive birefringence.

## **Correct Answer: C. Administer NSAIDs**