What is pannus and what are the appropriate treatment options for rheumatoid arthritis, prosthetic heart‑valve obstruction, and ocular involvement?

Pannus: Definition and Treatment Approaches

Pannus is an abnormal tissue growth composed of myofibroblasts and collagen fibers that has distinct treatment implications depending on its location—in rheumatoid arthritis, it requires aggressive disease-modifying therapy to prevent joint destruction, while in prosthetic heart valves, it necessitates surgical valve replacement rather than medical management.

Definition and Pathophysiology

Pannus manifests differently depending on anatomical location:

In Rheumatoid Arthritis

Pannus represents invasive granulation tissue that develops in the synovium and extends over articular cartilage surfaces 1. This tissue is pathologically central to joint destruction in RA, though the molecular mechanisms by which synovial fibroblasts maintain their aggressive phenotype remain incompletely understood 1. The pannus directly invades and destroys cartilage and bone, leading to the characteristic erosive changes of RA.

In Prosthetic Heart Valves

Pannus appears as fibrous tissue overgrowth composed of myofibroblasts and collagen fibers that develops around prosthetic valve structures 2. Critically, pannus can serve as a nidus for superimposed thrombus formation—nearly half of patients undergoing redo valve replacement for obstruction demonstrate combined thrombus and pannus 2.

On cardiac CT imaging, pannus characteristically appears as:

• A thin circular or crescentic hypodense rim located sub-valvularly
• Extends along the valve sewing ring
• Higher attenuation (HU ≥145) compared to thrombus 2, 3
• Occurs relatively late after valve implantation 2

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Treatment Approach for Rheumatoid Arthritis

Initial Disease-Modifying Therapy

Start methotrexate immediately upon RA diagnosis at 15 mg weekly, escalating to 20-25 mg weekly within 4-6 weeks 4, 5. This aggressive early approach is essential because pannus formation begins early and causes irreversible joint damage.

Treatment Escalation Algorithm

At 3 months post-initiation, assess disease activity using validated measures (SDAI or CDAI):

• If SDAI >11 (or CDAI >10): Add biologic DMARD or targeted synthetic DMARD

  • Options include TNF inhibitors, abatacept, IL-6 inhibitors (tocilizumab), or JAK inhibitors 5, 4
  • For patients ≥65 years with cardiovascular risk factors or smoking history, prioritize biologics over JAK inhibitors 6

• If inadequate response to first biologic: Switch to agent with different mechanism of action 5

  • Abatacept is more effective than placebo in TNF-inhibitor failures 5
  • Consider rituximab, tocilizumab, or alternative TNF inhibitor 1

Target Goals

Aim for remission (SDAI ≤3.3) or low disease activity (SDAI ≤11) 5. Patients achieving low disease activity at 3 months have >75% probability of remission at 1 year 5. Failure to suppress pannus formation leads to progressive joint destruction and disability.

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Treatment Approach for Prosthetic Valve Obstruction

Critical Diagnostic Distinction

The distinction between thrombus and pannus is essential because it fundamentally determines treatment strategy 2, 7, 2:

Thrombus characteristics:

• Lower attenuation on CT (HU <145) 2, 3
• Irregular morphology with independent mobility 2
• Associated with subtherapeutic INR 2
• Shorter duration from valve insertion to symptoms 8
• Typically presents acutely 8

Pannus characteristics:

• Higher attenuation on CT (HU ≥145) 2, 3
• Crescentic/circular morphology along sewing ring 2
• Sub-valvular location 2
• Occurs late after implantation (typically >10 years) 2, 9
• Gradual symptom onset 8

Diagnostic Workup

1. Initial evaluation: TTE and TEE echocardiography 2, 7
2. Definitive imaging: Cardiac CT with cine imaging 2
   • CT has 85% sensitivity for pannus (vs. 62% for TEE) 2
   • Fluoroscopy for mechanical valve leaflet motion assessment 2, 7

Treatment Algorithm

For PHV thrombosis (HU <145):

• Urgent treatment with either slow-infusion low-dose fibrinolytic therapy OR emergency surgery 7
• Recent protocols show >90% success rates with <2% embolic events using slow-infusion regimens 7
• Anticoagulation with vitamin K antagonist is reasonable for suspected valve thrombosis 10

For pannus obstruction (HU ≥145):

• Redo valve replacement is indicated for symptomatic severe stenosis 7, 10
• Medical management (anticoagulation/thrombolysis) is ineffective for pannus 2
• Surgical intervention is the only definitive treatment 2, 10

Risk Factors for Pannus Formation

• Young age at valve replacement 9
• Small prosthetic valve size 9
• Concomitant mitral valve replacement 9
• Cumulative incidence: 0.3% at 10 years, 5.0% at 20 years 9

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Ocular Pannus

While the provided evidence does not specifically address ocular pannus (corneal vascularization), this represents a distinct entity typically managed by ophthalmology with treatment directed at the underlying cause (contact lens overwear, trachoma, etc.) and is not directly related to the rheumatologic or cardiac manifestations discussed above.

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Common Pitfalls

1. Attempting medical management of prosthetic valve pannus: Unlike thrombus, pannus requires surgical intervention—anticoagulation and thrombolysis will fail 2

2. Delaying DMARD escalation in RA: The 3-month assessment is critical; failure to achieve low disease activity by this point predicts poor long-term outcomes 5

3. Relying solely on echocardiography for prosthetic valve obstruction: CT provides superior differentiation between thrombus and pannus 2, 3

4. Inadequate anticoagulation monitoring: 75.8% of prosthetic valve obstructions occur with INR <2.5 11