What is the role of hand ultrasound (US) in diagnosing and managing rheumatological conditions, such as rheumatoid arthritis (RA)?

Hand Ultrasound in Rheumatology

Hand ultrasound is essential in rheumatology for detecting subclinical synovitis, bone erosions, tenosynovitis, and crystal deposits that are frequently missed on clinical examination alone, using high-frequency transducers (≥10 MHz) to identify even minor inflammatory lesions in the wrist and finger joints. 1, 2

Primary Diagnostic Applications

Detection of Early Inflammatory Changes

• US detects subclinical synovitis and synovial proliferation in hand joints that clinical examination misses, particularly in early rheumatoid arthritis 3, 4
• High-frequency transducers of 10 MHz or higher can identify even minor synovitic lesions in the metacarpophalangeal (MCP) and interphalangeal (IP) joints 1
• Power Doppler imaging demonstrates active inflammation by detecting increased vascularity within the synovium 3, 4

Structural Damage Assessment

US identifies the following pathologies in hand joints 1:

• Bone erosions (often detected before conventional radiography shows changes) 3, 4
• Cartilage thinning and lesions 1
• Tendinitis, tenosynovitis, and tendon tears 1
• Synovial cysts and ganglia 1

Crystal Arthropathy Diagnosis

• US has significantly higher sensitivity than radiography for detecting calcium pyrophosphate deposition (CPPD) crystals at the wrist 5
• The wrist is a common target site for CPPD disease 5
• US can detect crystal deposits and calcinosis as periarticular lesions 1

Standardized Scanning Protocol

Patient Positioning

• Sitting position with the hand placed on top of the thigh or examining table 1, 6
• Dynamic examination with active flexion/extension of fingers should be performed 1, 6

Wrist Standard Scans

The following views are required 1, 6:

1. Volar transverse scan (visualizes median nerve at carpal tunnel)
2. Volar longitudinal scan
3. Dorsal transverse scans (radial and ulnar)
4. Dorsal longitudinal scans (radial, median, and ulnar)

Hand/Finger Standard Scans

Required views include 1:

1. Dorsal longitudinal scan
2. Dorsal transverse scan at metacarpal heads
3. Palmar longitudinal scans at MCP and IP joints
4. Palmar transverse scans at metacarpal heads

Differential Diagnosis Between RA and PsA

US patterns help distinguish rheumatoid from psoriatic arthritis based on location, distribution, and type of inflammatory findings 7:

Key Distinguishing Features

• Location of gray-scale inflammatory findings (RA typically affects MCP and PIP joints symmetrically; PsA often involves DIP joints) 7
• Periarticular soft tissue involvement (more prominent in PsA) 7
• Distribution and extent of Doppler signal (intra- vs peri-articular patterns differ) 7
• Shape and location of erosions (RA: marginal; PsA: central "pencil-in-cup") 7
• Tendon involvement without synovial sheath (more common in PsA) 7
• Entheseal involvement (characteristic of PsA) 7

Treatment Monitoring

• US monitors response to disease-modifying therapies by tracking changes in synovial thickness and Doppler signal 3, 4, 8
• Serial US examinations assess disease activity more sensitively than clinical examination alone 4, 8
• US guides therapeutic decisions by detecting persistent subclinical inflammation despite clinical remission 2, 8

Procedural Guidance

US guidance significantly improves accuracy of joint aspirations and intra-articular injections in hand joints 3, 4, 8:

• Particularly valuable for small joints where blind injection has lower success rates 4
• Essential when joint aspiration is difficult for synovial fluid analysis 5
• Increases safety by avoiding neurovascular structures 8

Additional Rheumatologic Applications

Carpal Tunnel Syndrome

• US differentiates synovial from tenosynovial pathology and examines median nerve morphology 1
• Volar transverse scan at the carpal tunnel has 77-79% sensitivity and 94-98% specificity for median nerve entrapment 6

Nerve Assessment

US evaluates 6:

• Median nerve enlargement and compression at the carpal tunnel
• Ulnar nerve at the elbow (cross-sectional area measurement)
• Radial nerve pathology (best visualized at the elbow)

Common Pitfalls to Avoid

• Do not rely on clinical examination alone in early inflammatory arthritis—US detects subclinical disease that alters management 3, 4
• Always use high-frequency transducers (≥10 MHz)—lower frequencies miss minor synovitic lesions 1
• Perform dynamic examination with finger flexion/extension—static imaging may miss tenosynovitis 1
• Examine both symptomatic and disease-specific target sites—CPPD and other conditions have characteristic distribution patterns 5
• Correlate US findings with clinical context—imaging abnormalities must be interpreted alongside patient history and examination 5

Clinical Integration

US should be performed at the time of consultation as an extension of clinical examination rather than as a separate imaging study 8:

• Allows immediate correlation of symptoms with anatomical findings 8
• Enables real-time patient education about disease process 8
• Facilitates immediate therapeutic decisions including guided injections 8

The evidence strongly supports US as the imaging method of choice for establishing early diagnosis, assessing disease activity, and monitoring treatment efficacy in inflammatory hand conditions 2, 8.