WBR0900

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathophysiology
Sub Category	SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::An obese 63-year-old male with history of dyslipidemia on statin and hypertension, treated with thiazide diuretics, presents with rapidly increasing pain in his big toe. The pain began in the morning and became progressively worse within the last 6 hours. Upon physical examination, the toe is observed to be erythematous, swollen, and tender upon palpation. The patient experienced two previous similar episodes, which resolved without treatment within a few days. Synovial fluid analysis reveals strongly birefringent needle-shaped crystals. Which of the following substances most likely composes the crystals?]]
Answer A	AnswerA::Uric acid
Answer A Explanation	[[AnswerAExp::The presentation of this patient is consistent with gouty arthritis. Hyperproduction or underexcretion of uric acid often leads to hyperuricemia predisposing gout. However, the crystal deposits in gouty arthritis are composed of monosodium urate.]]
Answer B	AnswerB::Monosodium urate
Answer B Explanation	AnswerBExp::The presentation of this patient is consistent with gouty arthritis, a condition characterized by deposition of monosodium urate crystals.
Answer C	AnswerC::Calcium pyrophosphate dehydrate
Answer C Explanation	[[AnswerCExp::Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease, also known as chondrocalcinosis, pseudogout, and pyrophosphate arthropathy, is a rheumatic disorder with varied symptoms and signs arising from the accumulation of crystals of calcium pyrophosphate dihydrate in the connective tissues. Pseudogout usually involves larger joints but can present similarly to gout. The presence of needle shape crystals, which are strongly birefringent, is characteristic of gout but not pseudogout.]]
Answer D	AnswerD::Phosphoribosylpyrophosphate
Answer D Explanation	[[AnswerDExp::Increased levels of phosphpribosylpyrophosphate (PRPP), frequently leads to the overproduction and accumulation of uric acid, resulting in hyperuricemia and hyperuricosuria. Increased levels of PRPP are often present in Lesch-Nyhan syndrome, which is characterized by decreased levels of hypoxanthine guanine phosphoribosyl transferase (HGPRT), responsible for purine salvage.]]
Answer E	AnswerE::Basic calcium phosphate
Answer E Explanation	AnswerEExp::The presentation of this patient is consistent with gouty arthritis. Gout is not characterized by basic calcium phosphate deposition in the joint.
Right Answer	RightAnswer::B
Explanation	[[Explanation::Gout is an inflammatory disease of the joint, characterized by the deposition of monosodium urate crystals. Gout is associated with hyperuricemia, resulting from either overproduction or underexcretion of uric acid. Triggers of gout include recent surgery, trauma, treatment with thiazide diuretics, high protein diet, and excessive alcohol intake. Often, acute symptoms associated with gout are treated with NSAIDs or colchicine. In addition to dietary modifications, long-term treatments of gout include medications such as xanthine oxidase inhibitors, in case of overproduction of uric acid, and uricosuric agents, in case of underexcretion. Educational Objective: Gouty arthritis is an inflammatory disease of the joint characterized by deposition of monosodium urate crystals. References: Tuhina N (2011). Gout. NEJM. 2011; 364:443-452]]
Approved	Approved::Yes
Keyword	WBRKeyword::Gout, WBRKeyword::Arthritis
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::