A 55-year-old man presented to his general physician with pain and swelling of his right great toe. He repoed he has had this pain for approximately 2 days and it is getting worse. He also stated that he had a similar episode of this 4 years ago, but in the interim, he has been symptom free. He was given something for the prior episode, but does not recall the name. He denied trauma, fever, chills or sweats, and has been afebrile. On physical examination, he was afebrile and his right great toe is swollen at the metatarsophalangeal joint. There was decreased range of motion. X-ray films are unrevealing. He had no other joint involvement. A joint aspiration is performed. Which of the following types of crystals in the joint aspirate would confirm the likely diagnosis?
A 55-year-old man presented to his general physician with pain and swelling of his right great toe. He repoed he has had this pain for approximately 2 days and it is getting worse. He also stated that he had a similar episode of this 4 years ago, but in the interim, he has been symptom free. He was given something for the prior episode, but does not recall the name. He denied trauma, fever, chills or sweats, and has been afebrile. On physical examination, he was afebrile and his right great toe is swollen at the metatarsophalangeal joint. There was decreased range of motion. X-ray films are unrevealing. He had no other joint involvement. A joint aspiration is performed. Which of the following types of crystals in the joint aspirate would confirm the likely diagnosis?
💡 Explanation
**Core Concept**
Gout is a form of inflammatory arthritis characterized by the deposition of monosodium urate (MSU) crystals within the joint space, leading to sudden onset of intense pain, swelling, and redness. This condition often presents with acute monoarthritis, typically affecting the base of the big toe (metatarsophalangeal joint).
**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of gout. In gout, there is an overproduction or underexcretion of uric acid, which leads to the formation of MSU crystals. These crystals are needle-shaped and negatively birefringent under polarized light microscopy. When MSU crystals are present in the joint aspirate, it confirms the diagnosis of gout. The presence of these crystals triggers an inflammatory response, which is responsible for the symptoms of gout.
**Why Each Wrong Option is Incorrect**
* **Option A:** Calcium pyrophosphate dihydrate (CPPD) crystals are associated with pseudogout, a condition that presents with sudden onset of joint pain and swelling, but typically affects multiple joints. CPPD crystals are rhomboid-shaped and weakly positively birefringent under polarized light microscopy.
* **Option B:** Ammonium urate crystals are associated with hyperuricemia, but they are not the primary crystals involved in gout. Ammonium urate crystals are not typically found in the joint aspirate of patients with gout.
* **Option D:** Uric acid crystals are not typically found in the joint aspirate of patients with gout. The correct name of the crystals associated with gout is monosodium urate (MSU) crystals.
**Clinical Pearl / High-Yield Fact**
Gout is a classic example of a "crystal-induced" arthritis. Remember that the presence of needle-shaped, negatively birefringent crystals in the joint aspirate confirms the diagnosis of gout.
**Correct Answer: C. Monosodium urate (MSU) crystals.**
✓ Correct Answer: A. Negatively-birefringent needle-shaped crystals.
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