What is the recommended treatment approach for a patient with psoriatic arthritis and latent tuberculosis (TB)?

Treatment of Psoriatic Arthritis in Patients with Latent Tuberculosis

Patients with psoriatic arthritis and latent TB must receive at least 1 month (preferably 3 weeks to 2 months) of isoniazid prophylaxis before initiating biologic therapy, and may start biologics while continuing the full 9-month prophylactic course if clinically urgent and the patient is adherent and tolerating treatment well. 1, 2

Mandatory Pre-Treatment Screening

All patients with psoriatic arthritis being considered for biologic or immunosuppressive therapy require tuberculosis screening 3, 2:

• Tuberculin skin test (TST) using the Mantoux method is the currently recommended screening method, with induration ≥5 mm considered positive in immunosuppressed patients or those about to start immunosuppressive therapy 3, 2
• Chest radiography must be performed to exclude active tuberculosis 1, 4
• QuantiFERON-TB Gold In-Tube assay may be used as an alternative or adjunct to TST 5, 4
• Complete medical history focusing on TB exposure, prior TB treatment, and risk factors 1, 2

Latent TB Prophylaxis Protocol

When latent TB is diagnosed (positive screening without active disease):

• Isoniazid 300 mg daily for 9 months is the standard prophylactic regimen 3, 5, 4
• Start prophylaxis at least 1 month before biologic therapy when possible 1, 2
• If urgent psoriasis/arthritis control is required, biologics may be initiated after 3 weeks to 2 months of prophylaxis, provided the patient is strictly adherent and tolerating the regimen 1, 5, 2
• The full 9-month prophylactic course must be completed even after starting biologics 5, 4

Psoriatic Arthritis Treatment Selection

For Peripheral Arthritis with Latent TB:

Step 1: Initial therapy while awaiting TB clearance

• NSAIDs for symptom relief 3, 6
• Intra-articular glucocorticoid injections for persistently inflamed joints 3, 6
• Conventional synthetic DMARDs (csDMARDs) can be initiated: methotrexate (preferred if significant skin involvement), sulfasalazine, or leflunomide 3, 6

Step 2: After adequate TB prophylaxis (≥1 month)

• TNF inhibitors (etanercept, adalimumab, infliximab) for inadequate response to csDMARDs 3, 6, 7
• IL-17 inhibitors may be preferred when significant skin involvement exists 3
• IL-12/23 or IL-23 inhibitors are alternatives with relevant skin disease 3
• JAK inhibitors for inadequate response to both csDMARDs and biologics 3

Critical Safety Considerations for Biologics:

TNF inhibitors carry the highest TB reactivation risk and require the most stringent TB screening and prophylaxis 7, 1, 2:

• Etanercept (Enbrel) FDA labeling explicitly states: "Treatment of latent tuberculosis infection prior to therapy with TNF-blocking agents has been shown to reduce the risk of tuberculosis reactivation during therapy" 7
• Tests for latent TB may be falsely negative while on TNF-blocker therapy 7
• Induration of 5 mm or greater should be considered positive when assessing need for latent TB treatment prior to TNF inhibitors, even in BCG-vaccinated patients 7
• Anti-tuberculosis therapy should be considered even in patients with negative testing but TB risk factors 7

For Axial Disease with Latent TB:

• NSAIDs and physical therapy as first-line 3, 8
• TNF inhibitors for inadequate response to NSAIDs (after adequate TB prophylaxis) 3, 8
• IL-17 inhibitors may be preferred with significant skin involvement 3

Monitoring During Treatment

Ongoing TB surveillance is mandatory 7, 4:

• Close monitoring for signs/symptoms of infection during and after biologic therapy 7
• Periodic TB screening during therapy, as tests may become falsely negative on TNF inhibitors 7
• Annual tuberculosis screening recommended for patients on biologics 9
• Retesting at 31 months showed QFT-GIT reversion in 25% and conversion in 0.8% of patients 4

Evidence on Safety and Efficacy

Real-world data strongly supports this approach:

• In 56 psoriatic patients with latent TB receiving 9-month isoniazid prophylaxis starting 3 weeks before biologics, 54/56 (96%) completed prophylaxis without adverse events, and none developed active TB during long-term biologic therapy 5
• Only 1/56 patients developed TB pleurisy (on etanercept), which was successfully treated with subsequent safe biologic resumption 5
• In 243 psoriasis patients screened, 8.2% had latent TB; after isoniazid prophylaxis, none developed active TB during mean 37 weeks of biologic therapy 4
• The prevalence of latent TB in psoriasis patients (8.2%) is similar to healthcare workers (8.8%), emphasizing the importance of universal screening 4

Critical Pitfalls to Avoid

• Never start TNF inhibitors without TB screening - this is the highest-risk biologic class for TB reactivation 7, 1, 2
• Never add a single drug to a failing TB treatment regimen - always add ≥2 drugs to prevent resistance 3
• Do not rely on negative TB tests in patients already on immunosuppression - tests may be falsely negative 7
• Do not inject glucocorticoids through psoriatic plaques - risk of infection 6
• Do not assume 1 month of prophylaxis is sufficient - the full 9-month course must be completed 5, 4