Usefulness of ultrasound in the diagnosis of crystal deposition diseases

Abstract

Gout and calcium pyrophosphate crystal deposition disease (CPPD) are common forms of inflammatory arthritis whose prevalence has increased in recent years. Although the identification of monosodium urate crystals (MSU) and calcium pyrophosphate crystals (CPP) in synovial fluid (SF) by polarized light microscopy are the gold standard for diagnosing these diseases, SF analysis is not always available. An early diagnosis and specific treatment, especially in gout, allows avoiding irreversible structural damage, comorbidities, and a severe impact on the quality of life of patients. Musculoskeletal ultrasound (US) is a noninvasive tool that allows detecting aggregates of microcrystals at multiple anatomical sites and helps to establish a specific diagnosis. The objective of this review is to evaluate the applications of US in the diagnosis and clinical management of the main microcrystalline arthropathies. The US has helped improve our understanding of the natural history of the disease, due to its ability to visualize not only soft tissue inflammation and structural damage, but also the characteristics of MSU and CPP crystal deposition. The anatomical sites of crystal deposition are also a key factor for differential diagnosis in different microcrystalline diseases. The US allows establishing an early diagnosis, especially in asymptomatic hyperuricemia, to discriminate with other inflammatory diseases, to assess the extent of microcrystalline deposition and their sensitivity to change after treatment. Given its increasing availability in clinical practice and strong evidence, US is a bedside imaging technique helping clinicians to improve diagnosis and therapy monitoring in their daily practice.

Figure 1.

EULAR three-step approach for the diagnosis of gout.

Figure 2.

Double contour sign (DCS). Hyperechoic enhancement of the chondrosynovial interface secondary to the monosodium urate crystal deposition. Transversal scan of the femoral cartilage surface.

Figure 3.

Double contour sign (DCS). Longitudinal view of the dorsal aspect at the first metatarsophalangeal joint in a gout patient.

Figure 4.

Tophus on proximal patellar tendon (arrow). Note the circumscribed, inhomogeneous, hyperechoic aggregation, without acoustic shadow.

Figure 5.

Tophus (*) in the wrist volar region on the flexor tendons, surrounded by an anechoic halo (arrows).

Figure 6.

Tophus may generate posterior acoustic shadow (*) due to the crystal density of MSU crystals.

Figure 7. A, B.

(A) Patient with gout. Longitudinal image of the quadriceps tendon enthesis. A tophus is observed on the tendon (*) and hyperechoic aggregates in its enthesis (arrow). (B) Other case of gout patient. The quadriceps tendon inserting into the patella in a longitudinal scan. The image showing loss of the typical fibrillar pattern, enthesophytes, and hyperechoic aggregates within the tendon (arrow).

Figure 8.

Bone erosion in a patient with gout (*) of extraarticular location and adjacent to intratendinous aggregates (**) in the triceps enthesis in the elbow. Several tophi and aggregates are seen inside the olecranon bursa (arrow).

Figure 9. A, B.

(A) Cortical erosion (arrow) in the calcaneus at the insertion of the Achilles tendon (longitudinal plane). (B) transverse plane). A tophus is observed related to the enthesis (*).

Figure 10.

First episode of acute gouty arthritis in the first metatarsophalangeal joint with synovial effusion in the bursa (*). Metatarsal head already has an erosion in the bone cortex (arrow).

Figure 11.

Synovitis with intense Doppler signal in an acute inflammatory episode of gout in second metacarpophalangeal joint.

Figure 12. A, B.

(A) Triceps tendon enthesis of the elbow with adjacent tophus in grayscale (arrow). (B) In the color Doppler image, an intense Doppler signal is observed in the tophus. The patient did not report symptoms in the elbow.

Figure 13.

Knee hyaline cartilage CPP deposits (arrows). Hyperechoic (similar to the cortical bone echogenicity) without posterior acoustic shadow localized within the hyaline cartilage.

Figure 14. A-D.

(A) and (B) Hyperechoic aggregates in carpal triangular fibrocartilage characteristic of CPPD (*). (C) Aggregates in fibrocartilage of the acromioclavicular joint. (D) Aggregates in the meniscus of the knee.

Figure 15.

Patient with CPPD and double contour image in the second metacarpophalangeal joint of the hand (arrow).

Figure 16. A-F.

Patient with tophaceous or pseudotumoral CPPD in the wrist. (A) Conventional CT image showing calcium aggregates (*) and bone erosions (arrows). (B) Conventional radiography of the hand with chondrocalcinosis in the carpal triangular fibrocartilage (arrow). (C) Ultrasonographic image of carpal extensor tendons with aggregates similar to tophus (*). (D) Surgical image of the aggregates (courtesy Dr. Xavier Gonzalez), histology confirmed that they were CPP crystals. (E) and (F) Ultrasound images of the wrist with intrasynovial hyperechoic aggregates (*).

Figure 17.

Longitudinal ultrasound image of the supraspinatus tendon with an aggregate of crystals of basic calcium crystals (*).