What SH 1 and PD Mean During MSK Ultrasound
SH 1 indicates mild synovial hypertrophy (grade 1 thickening of the joint synovium), while PD refers to power Doppler signal indicating active inflammation and increased blood flow within the synovium.
Understanding the Terms
Synovial Hypertrophy (SH)
According to EULAR standardized terminology, synovial hypertrophy is defined as hypoechoic thickening of the synovium detected on grayscale (B-mode) ultrasound 1. This is typically graded on a semiquantitative scale from 0-3:
- Grade 0: No synovial thickening
- Grade 1: Mild synovial thickening (SH 1)
- Grade 2: Moderate synovial thickening
- Grade 3: Severe synovial thickening
SH 1 represents the mildest detectable degree of synovial thickening above normal limits.
Power Doppler (PD)
Power Doppler signal represents increased blood flow (synovial hyperemia) within the thickened synovium 1. Histopathologic studies confirm that PD signals correlate with active inflammation, showing significantly more lymphocyte infiltration, vessel proliferation, and lining hyperplasia compared to PD-negative synovium 2.
PD is also graded 0-3 based on the amount of vascular signal detected within the synovial tissue.
Clinical Significance
Prognostic Implications
The presence of both SH and PD carries important prognostic information:
- PD activity is strongly predictive of disease progression. In rheumatoid arthritis patients in clinical remission, PD synovitis increases the odds of radiographic progression by 12-fold (OR 12.21, p<0.001) 3
- SH alone (even without PD) is also predictive, with a 2.3-fold increased odds of radiographic progression (OR 2.31, p=0.032) 3
- Patients with PD activity have higher relapse rates: 47.1% versus 20.0% in those without PD signal (p=0.009) 3
Important Clinical Considerations
Subclinical inflammation is common: Even grade 1 synovial hypertrophy without Doppler activity can represent active disease that responds to treatment 4. Studies show that joints with SH but no PD signal still improve significantly during disease-modifying therapy, indicating these findings should not be dismissed as inactive disease.
Age and gender affect normal ranges: In asymptomatic individuals, mild synovial thickening can be present, particularly in elderly patients and varies by gender 5, 6. However, any PD signal is uncommon in healthy controls (present in only 0-1.2%) 6, making PD activity a more specific marker of pathologic inflammation.
Practical Application
When you see SH 1 with PD activity on a report:
- This indicates mild synovial thickening with active inflammation
- Consider this a sign of active disease requiring treatment optimization, even if the patient appears clinically well
- This combination predicts future joint damage and disease flares
- Follow-up imaging can assess treatment response
When you see SH 1 without PD:
- Still represents abnormal findings that may indicate subclinical disease activity
- Less predictive of progression than when PD is present, but not benign
- Consider clinical context, as this can be sensitive to treatment changes 4
The combination of grayscale synovial hypertrophy grading and power Doppler assessment provides complementary information about both structural changes and active inflammation in the joint 1.