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Gout

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Authors

John Kiel DO, MPH
Assistant Professor of Emergency Medicine
Assistant Professor of Sports Medicine
University of Florida College of Medicine – Jacksonville

Gurjit Kaeley, MD
Professor of Rheumatology
University of Florida College of Medicine – Jacksonville

Summary

  • Ultrasound represents an easy way to support or refute the diagnosis of gout
  • Upside: It is quick, easy to perform and can reduce need for arthrocentesis, advanced imaging and time in emergency department
  • Downside: it requires an experienced sonographer and evaluation of multiple joints
Video showing large complex effusion and bony irregularity inferior to the overlying flexor tendon sheath. The tendon glides freely and independent of the underlying joint effusion. Note: Gout was proven by aspiration.

Introduction

  • Gout is a painful crystal arthropathy and common cause of monoarticular joint pain affecting up to 3% of adults in the US[1]Smith E, Hoy D, Cross M, et al. The global burden of gout: estimates from the Global Burden of Disease 2010 study. Ann Rheum Dis 2014.
  • Gout is characterized by monosodium urate (MSU) crystal deposition in the synovial fluid of joints secondary to elevated uric acid.
  • Gout presents as joint pain. In men, the most common joints affected include the first metatarsophalangeal (MTP) joint (referred to as podagra), ankle and knee, although any joint can be affected. Women tend to present later in life with polyarticular manifestations.
  • Acute flares present as sudden onset of pain, often following consumption of protein heavy meals or alcohol.
  • In chronic cases, tophaceous gout is characterized by chronic inflammation, hyperuricemia. Subsequently, MSU crystals are deposited into joints, bursa, and tendons and can affect a variety of extra-articular soft tissue[2]Grassi W, De Angelis R. Clinical features of gout. Reumatismo. 2012;63(4). doi:10.4081/reumatismo.2011.238.
  • Gout is traditionally diagnosed by history, physical exam, serum uric acid levels and the presence of MSU crystals in synovial fluid analysis[3]Neogi T, Jansen TLTA, Dalbeth N, et al. 2015 Gout Classification Criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative: Acr/Eular classification … Continue reading

Sonographic Evaluation

  • Ultrasound (US) represents a novel method of evaluating and diagnosing gout in the emergency department (ED).
  • Deposition of MSU crystals have sonographically unique features and may be seen intra-articular or in extra-articular soft tissues including tendon and bursa.
  • Intra-articular urate deposition can affect articular cartilage, leading to intra-articular aggregates and tophus.
  • The ‘double contour’ sign refers to deposition of MSU crystals within the cartilage surface. It is characterized by an irregular, echogenic line on the outer edge of articular cartilage independent of the angle of insonation. This finding is specific to gout and a component of the ACR gout classification [4]Neogi T, Jansen TLTA, Dalbeth N, et al. 2015 Gout Classification Criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative: Acr/Eular classification … Continue reading.
  • Tophaceous deposits can be readily identified on US. Most tophi are hyperechoic and heterogeneous, sometimes referred to as ‘snowstorm’ appearance. In some cases, they may have hypoechoic areas. An anechoic border can range from sonolucent to sono-opaque in appearance[5]Nalbant S, Corominas H, Hsu B, Chen LX, Schumacher HR, Kitumnuaypong T. Ultrasonography for assessment of subcutaneous nodules. J Rheumatol. 2003;30(6):1191-1195..
  • Additional potential intra-articular findings include synovial effusion, synovial hypertrophy, increased color flow, and doppler signal. These findings are nonspecific to gout.
  • Extra-articular findings are also common but may but may be asymptomatic and not identified on initial presentation. Most commonly, this will present as urate deposition within the patellar and achilles tendon.
  • Sonographically, this appears as hyperechoic, heterogeneous signal within the ligament. These are often accompanied by the other intra-articular findings described above.
  • There is literature to support the use of US in the diagnosis of gout.
  • Chowalloor et al found the US was useful to assess tophi, double counter sign and joint erosions[6]Chowalloor PV, Keen HI. A systematic review of ultrasonography in gout and asymptomatic hyperuricaemia. Ann Rheum Dis. 2013;72(5):638-645.. They found the double contour sign to be specific, but not sensitive.
  • Zhang et al found the double contour sign to be 66% sensitive and 92% specific, tophi to be 56% sensitive, 94% specific and snowstorm sign to be 31% sensitive, 91% specific [7]Zhang Q, Gao F, Sun W, Ma J, Cheng L, Li Z. The diagnostic performance of musculoskeletal ultrasound in gout: A systematic review and meta-analysis. PLoS One. 2018;13(7):e0199672.. If the three signs are pooled together, the sensitivity increases to 80%. Zhang et al also found that the presence of these sonographic features correlated to serum uric acid levels.
  • Zhu et al found hyperechoic aggregates and the double contour sign found in combination improves the specificity to 97%[8]Zhu L, Zheng S, Wang W, Zhou Q, Wu H. Combining hyperechoic aggregates and the double-contour sign increases the sensitivity of sonography for detection of monosodium urate deposits in gout: … Continue reading.
Knee US Prox Pat Ligament Normal
Normal proximal patella tendon as seen in long axis.
Knee US Prox Patellar Ligament Gout
Abnormal patella tendon in long axis with tophaceous deposits in the patellar tendon (arrow) consistent with gout.
Knee US Distal Patellar Ligament Normal
Normal distal patella tendon in long axis.
Knee US Distal Patellar Ligament Gout
Abnormal patella tendon in long axis with tophaceous deposits (arrow) consistent with gout.
Knee US Knee Max Flex Normal
Sonogram of the femoral condyle in short axis with the knee in maximal flexion. The interface sign (arrow) is noted and should not be confused with the double contour sign.
Knee US Double Contour Sign of the Knee
View of the knee in max flexion with double contour sign (arrow) consistent with gout.
Toe US Plantar Metatarsal Head Normal
Normal sonogram of the plantar surface of the 1st metatarsal head in long axis. The interface sign (arrow) is noted and should not be confused with the double contour sign.
Toe US Plantar MTP Double contour
Short axis of the 1st metatarsal head on the plantar surface with double contour sign (arrow) consistent with gout.
Toe US Dorsal MTP 1 Normal
Normal long axis of dorsal 1st metatarsophalangeal (MTP) joint  showing articular cartilage (arrow) and edge of capsule (asterisk). The interface sign (arrow) is noted and should not be confused with the double contour sign.
Toe US Dorsal MTP Gout
Long axis view of 1st MTP joint showing significant intra-articular tophi (arrow) consistent with gout.

Benefits

  • Quick, easy to perform
  • Potentially avoid unnecessary laboratory analysis, painful arthrocentesis
  • Reduce cost of advanced imaging
  • Reduced time in emergency department
  • May help expedite follow up with rheumatology, especially if tophaceous gout is identified
  • Opportunity for aspiration to exclude septic arthritis

Challenges

  • Requires experienced sonographer
  • Often requires evaluation of multiple joints which may require more time in the context of a busy emergency department

Pearls and Pitfalls

  • Mistakenly believing cartilage ‘interface sign’ is the ‘double contour sign’
  • With high contrast equipment, overcalling heterogeneous aggregates
  • Not examining the joint sufficiently to exclude extrasynovial deposition

Read More

Special thanks to Dr Kaeley for sharing these images.

References

References[+]