Diagnosis And Differential Diagnosis Of Common Crystal Arthropathies

In the diagnosis of gout, is synovial fluid crystal analysis necessary for symptomatic patients?

The 2023 EULAR imaging guidelines for the diagnosis and treatment of CiAs indicate that when characteristic manifestations of MSU deposition are identified on ultrasound (i.e., double contour sign or tophi) or DECT, gout can be diagnosed without synovial fluid analysis.

• Although evidence of MSU deposition in synovial fluid or tissue analysis remains a diagnostic hallmark, it may not always be feasible due to unsuccessful joint aspiration or lack of facilities/expertise for analyzing joint fluid.

• However, as a general rule, joint aspiration should always be attempted whenever feasible, especially to exclude other causes of acute arthritis, such as septic arthritis, regardless of whether there is previous evidence of gout (e.g., DECT positive and hyperuricemia).

• Gout may coexist with septic arthritis or CPPD, which again requires synovial fluid to exclude/confirm differential diagnoses.

• Imaging findings should be interpreted with care, considering that they are not completely specific (i.e., the double contour sign is a typical feature of gout but may be present in CPPD and asymptomatic hyperuricemia).

➤ Exists in >25% of CPPD patients

➤ Commonly involves one or more large joints, with the knee and wrist being the most severely affected, and less commonly the MTP1

Over time, other joints may be affected

➤ Any joint may be involved, and polyarthritis may occur

➤ Typically presents as intermittent, acute, self-limiting, severe joint redness, swelling, and pain, with asymptomatic periods in between

➤ Patients often have systemic manifestations, including fever, leukocytosis, elevated ESR, and other acute-phase reactants

➤ It takes longer to reach peak intensity, and symptoms may persist for up to 120 days despite treatment

➤ Differential diagnosis: infection, trauma, hemorrhage, and other crystal-related diseases (such as gout), further synovial fluid analysis can assist in disease differentiation.

➤ Is a common chronic manifestation of calcium pyrophosphate crystal deposition disease

➤ A large portion of CPPD patients have degenerative arthritis

➤ Affects joints similar to OA

➤ Commonly involves the knee, wrist, MCP, hip, and shoulder joints, presenting as gradually onset pain and slowly progressive joint destructive inflammatory symptoms, with morning stiffness and synovitis being rare

Half of the patients will have superimposed acute arthritis attacks

➤ Differentiation from OA:

• The affected joints are usually not the typical joints involved in pure OA patients

• When occurring in the knee joint: primary OA is more common in the medial compartment, leading to varus deformity; OA with CPPD or elderly pseudosecond OA is more likely to affect the lateral compartment and lead to valgus deformity;

• Significant degenerative joint lesions usually have calcification of cartilage as a preceding manifestation

➤ Manifestations are similar to RA: significant morning stiffness, fatigue, synovial thickening, localized edema, and restricted joint movement caused by active inflammation or flexion contracture

➤ Affects multiple joints – peripheral joints of the upper and lower limbs

• Including wrist joints, metacarpophalangeal joints, knee joints, and elbow joints

➤ Symmetrical or nearly symmetrical distribution

➤ Arthritis can last for months, and the inflammation of the affected joints often varies in severity and is unrelated

• Multiple inflammatory joints usually flare up independently

➤ These episodes are usually self-limiting, often lasting from days to weeks

➤ Differentiation from RA:

• In RA patients, multiple joint inflammation often occurs simultaneously and resolves

• Compared to RA, chronic CPP crystal inflammatory arthritis has radiological changes more similar to OA, but the clinical manifestations of the affected joints are more like RA

➤ The imaging characteristics may resemble neuropathic joint destruction

➤ However, true neuropathic joint destruction is characterized by loss of joint position sense, occasionally accompanied by loss of other sensations (such as pain and temperature sense)

➤ Clinical manifestations include spinal stiffness, sometimes leading to joint bony ankylosis, resembling spinal lesions of AS or DISH

• This type of symptom is most common in familial CPPD disease

➤ Crystal deposition in the yellow ligament at the cervical level or lower posterior longitudinal ligament can lead to spinal cord compression syndrome or cause acute nerve compression symptoms or chronic spinal canal stenosis symptoms

• The space-occupying effect caused by CPPD crystals and associated soft tissue accumulation must be differentiated from other calcified or ossifying space-occupying lesions

➤ Odontoid process plus crown syndrome (CDS)