Crystal Arthropathies
Rheumatology · Crystal Arthropathies 🎯 Practice these cards
MSU crystals are ____-shaped and ____ birefringent (yellow when parallel to the axis).
Monosodium urate (MSU) crystals, which cause gout, are needle-shaped and negatively birefringent: they appear yellow when parallel to the polarizing axis and blue when perpendicular.
CPP crystals are ____-shaped and ____ birefringent (blue when parallel to the axis).
Calcium pyrophosphate (CPP) crystals, which cause pseudogout, are rhomboid-shaped and positively birefringent: they appear blue when parallel to the polarizing axis and yellow when perpendicular.
The saturation point of serum urate at physiologic temperature and pH is ____ mg/dL.
At physiologic temperature and pH, the saturation point of serum urate is 6.8 mg/dL (0.40 mmol/L); below this, MSU crystals dissolve. Solubility falls in cool, acidic distal tissues, explaining the predilection for the great toe.
The ACR treat-to-target serum urate goal in gout is below ____ mg/dL.
Urate-lowering therapy aims for a serum urate below 6.0 mg/dL (0.35 mmol/L); EULAR recommends below 5.0 mg/dL (0.30 mmol/L) in patients with tophi.
Acute flare colchicine dosing is ____ mg initially, then ____ mg one hour later.
The simplest acute gout flare regimen is colchicine 1.2 mg at the first symptom, followed by 0.6 mg one hour later; it is most effective within 24 hours of onset.
Before starting allopurinol, test for the ____ allele in patients of Southeast Asian and African descent.
The HLA-B*58:01 allele markedly increases the risk of allopurinol hypersensitivity (DRESS/DIHS). The 2020 ACR guideline conditionally recommends testing before starting allopurinol in patients of Southeast Asian (Han Chinese, Thai, Korean) and African descent.
Chondrocalcinosis prevalence ____ with every decade past age ____ years.
Chondrocalcinosis prevalence doubles with every decade past age 60, and nearly half of patients in their late 80s have CPP visible on radiographs. CPPD in a patient under 50 warrants a metabolic workup.
Two metabolic causes of CPPD to check in a young patient are hyperparathyroidism and ____.
In a young patient with CPPD, evaluate for hyperparathyroidism, hemochromatosis, hypophosphatasia, and hypomagnesemia.
Pegloticase should be discontinued if the serum urate exceeds ____ mg/dL on two consecutive pre-infusion checks.
Pegloticase (a uricase infused every 2 weeks) drives serum urate to near zero, but 30%–50% of patients develop anti-drug antibodies within weeks, abolishing efficacy and raising anaphylaxis risk. Discontinue if serum urate exceeds 6.0 mg/dL on two consecutive checks.
In the MIRROR RCT, co-prescribing ____ with pegloticase raised the month-6 responder rate to 71% vs 39%.
The MIRROR RCT showed that adding methotrexate (15 mg/week) to pegloticase raised the month-6 responder rate to 71% versus 39% with placebo, by suppressing anti-PEG anti-drug antibodies (25% vs 58% positive). This is now standard for refractory gout.
Anti-inflammatory prophylaxis when starting ULT should continue for at least ____ to ____ months.
When urate-lowering therapy is started, anti-inflammatory prophylaxis (usually colchicine 0.6 mg once or twice daily) should be continued for at least 3 to 6 months to prevent mobilization flares.
Basic calcium phosphate deposition classically causes "____ shoulder," and its crystals are visualized with ____ red stain.
Basic calcium phosphate (hydroxyapatite) deposition classically causes "Milwaukee shoulder" — a destructive inflammatory arthritis/periarthritis of the shoulder in older women. BCP crystals are too small for routine light microscopy and are seen only as alizarin-red–stained aggregates.
Tap a card to flip it.