Gout-PsA overlap warrants new look at disease mechanisms, role of urate crystals
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Psoriatic arthritis and gout often present with similar symptoms and radiological signs, an overlap that may be more significant when these diseases occur concomitantly, noted a presenter at the 2020 Congress of Clinical Rheumatology-West.
Differentiating between PsA accompanied by hyperuricemia and a gouty arthropathy with psoriasis — especially among patients with advanced radiological lesions — “is often challenging for clinicians, and in particular, rheumatologists,” Georg Schett, MD, head of the department of internal medicine 3 at the University Erlangen-Nürnberg, in Germany, told attendees.
This diagnostic challenge was recently thrust into the spotlight by Felten and colleagues in their 2020 study in Clinical Rheumatology , which depicted a patient with long-term oligoarthritis and psoriasis, a serum uric acid level of 9.3 mg/dL and a high CRP of 27 mg/L.
Schett noted that, in conventional X-rays of the hands, corrosive lesions and destruction of the distal interphalangeal joint of the hands were observed. Examination of the patient’s feet showed some nail involvement due to psoriasis, “but nail involvement that also bears involvement of the joint,” he said.
“Potentially, this can only be explained by psoriasis,” Schett said. “However, in this case, the [clinicians] found that there was uric acid crystals involved, and treated the patient with uric acid lowering drugs. I think this is very important: Sometimes, patients with PsA are receiving treatment with drugs like TNF inhibitors, but then they flare. One could think ‘well that is uncontrolled psoriatic arthritis’ when, in fact, it’s not the psoriatic arthritis that flares but its concomitant gout.”
Schett noted that Felten and colleagues coined the term “psout” to describe this unusual convergence of PsA and gout, linked by the involvement of urate crystals, “at the boundary between inflammatory and metabolic rheumatism.” In their study, Felten and colleagues suggested that “the concurrence of these two diseases should be seen as a novel overlap syndrome.”
The signs and symptoms associated with gout and PsA can be remarkably similar, according to Schett, and share otherwise telltale signs of “oligoarticular involvement, [distal interphalangeal] involvement and asymmetric arthritis, sometimes with erythema.”
Additionally, patients with gout have been known to exhibit dactylitis, which is frequently found in patients with PsA, whereas metatarsophalangeal involvement is frequently observed in gout and can be possible in PsA. Schett noted that “there is no real axial differentiation” since axial involvement in gout is rare but can occur and is more frequent in PsA. Although hyperuricemia is very frequent in gout “except in the flare” — it is known to occur in 30% of patients with PsA, without any diagnosis of gout.
“Urate crystals, of course, are well known in gout but are also found in 3% of PsA patients; this suggests there is a coincidence of the two diseases,” Schett said. “As you know, it is often difficult to detect the crystals directly if there is not enough effusion, so there is probably a much higher prevalence of [monosodium urate]-positive PsA patients than we often think.”
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Schett G. Gout – What’s New in 2020? Presented at: Congress of Clinical Rheumatology-West annual symposium; October 8-11, 2020 (virtual meeting).
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