What are the key clinical features that differentiate pseudogout from gout in a patient presenting with acute joint pain?

When differentiating pseudogout from gout in a patient presenting with acute joint pain, several key clinical features are important to consider.

The fundamental difference lies in the underlying crystal deposition: gout is caused by monosodium urate crystals, whereas pseudogout, also known as calcium pyrophosphate deposition (CPPD) disease, is caused by calcium pyrophosphate (CPP) crystals ¹ (Ferrone et al., 2012).

Regarding joint involvement, gout classically presents as a monoarthritis affecting the first metatarsophalangeal (MTP) joint of the big toe, though it can also affect other joints such as the ankle, knee, wrist, and elbow ¹,². In contrast, pseudogout more commonly affects larger joints, including the knee, wrist, and shoulder (Ferrone et al., 2012).

While both conditions can cause acute, severe joint pain, gout attacks typically have a very rapid onset, often peaking within 6 to 12 hours, and usually resolve within 7 to 10 days ¹. Pseudogout attacks can also be acute, but may sometimes present with a less dramatic inflammatory response or as a chronic arthropathy (Ferrone et al., 2012).

Associated risk factors also differ: gout is strongly linked to hyperuricaemia, obesity, metabolic syndrome, chronic kidney disease, and certain medications like diuretics ¹. Pseudogout is more frequently associated with older age, osteoarthritis, and metabolic conditions such as hyperparathyroidism, hemochromatosis, and hypomagnesemia (Ferrone et al., 2012).

Definitive diagnosis for both conditions relies on synovial fluid analysis: gout is confirmed by the presence of negatively birefringent, needle-shaped urate crystals, while pseudogout is confirmed by positively birefringent, rhomboid-shaped CPP crystals ¹ (Ferrone et al., 2012). Additionally, imaging findings such as chondrocalcinosis (calcification of articular cartilage) on X-ray are characteristic of pseudogout but not gout (Ferrone et al., 2012).