What interstitial and obstructive lung diseases are associated with psoriatic arthritis, and how should they be screened and managed?

Lung Disease Associated with Psoriatic Arthritis

Psoriatic arthritis is associated with both interstitial lung disease (ILD) and chronic obstructive pulmonary disease (COPD), with ILD occurring in approximately 10% of psoriasis patients and COPD risk increased 1.75-fold compared to controls.

Interstitial Lung Disease in Psoriatic Arthritis

Prevalence and Patterns

• ILD occurs in approximately 10% of patients with psoriasis, affecting both those with psoriasis vulgaris and psoriatic arthritis equally 1
• The most common radiographic pattern is indeterminate for usual interstitial pneumonia (UIP), followed by nonspecific interstitial pneumonia (NSIP) 1, 2
• Ground-glass opacities or consolidation appear in 25% of patients, with airway disease in 8-9% and interstitial fibrosis in 3-7% 3
• UIP pattern shows statistically significant higher frequency in smokers with psoriatic disease 2

Clinical Presentation and Prognosis

• Respiratory symptoms are present in 80% of patients with psoriatic arthritis-associated ILD 2
• The prognosis is generally favorable: over a median 8.9-year observation period, ILD progressed in only 42% of patients, with no cases of respiratory failure or death directly attributable to ILD progression 1
• However, airway disease and ground-glass opacities are strongly linked to death or transplant (hazard ratios of 2.07 and 2.50, respectively) 3

Chronic Obstructive Pulmonary Disease

Risk Magnitude

• The incidence rate ratio for developing COPD is 1.75 (95% CI 1.35-2.26) in patients with psoriatic arthritis compared to controls 4
• In a large meta-analysis, the pooled odds ratio for COPD in psoriatic patients was 1.45 (95% CI 1.21-1.73) 4
• Among current smokers with psoriasis, the odds ratio for COPD increases dramatically to 5.56 (95% CI 4.95-8.24) 4

Pathophysiology

• COPD in psoriatic arthritis represents end-organ damage from chronic inflammation, scarring, and loss of pulmonary elasticity 4
• The association persists even after adjusting for smoking, obesity, and socioeconomic status, suggesting psoriasis is an independent risk factor 4

Screening Recommendations

Initial Evaluation at Diagnosis

• Perform baseline chest radiography and serum Krebs von den Lungen-6 (KL-6) testing at the initial diagnosis of psoriatic arthritis 1
• Obtain baseline pulmonary function tests (spirometry and DLCO) for all patients with psoriatic arthritis 4
• Serum KL-6 levels are elevated in patients with ILD compared to those without ILD and serve as a useful screening biomarker 1

Risk Stratification for ILD Screening

High-risk patients requiring HRCT screening include those with:

• Pre-existing lung disease 4
• Age >40 years and current cigarette smoking 4
• Respiratory symptoms (dyspnea, cough) 4
• Abnormal pulmonary function tests 4
• Elevated serum KL-6 levels 1

Monitoring Strategy

For high-risk or symptomatic patients:

• Perform annual pulmonary function tests (spirometry and DLCO) 4
• Obtain HRCT every 2 years if risk factors are present 4
• Repeat HRCT if pulmonary function tests become abnormal or respiratory symptoms develop 4

For low-risk asymptomatic patients:

• Perform pulmonary function tests only when symptoms develop 4
• Clinical assessment for respiratory symptoms at every clinic visit 4

Critical Management Considerations

Methotrexate Safety

• Pre-existing lung disease, psoriatic arthritis, and cigarette smoking are documented risk factors for methotrexate-induced interstitial lung disease 4
• Discontinue methotrexate immediately if acute respiratory symptoms develop (cough, dyspnea, fever) suggesting drug-induced pneumonitis 5
• The 2023 ACR/CHEST guideline conditionally recommends continuing methotrexate in patients with mild and stable ILD who are already receiving it for joint disease, rather than switching to an alternative DMARD 5
• Patients with a history of drug-induced ILD are more susceptible to developing another ILD when treated with biologics, including IL-17 inhibitors 6

Biologic Therapy Considerations

• Drug-induced ILD has been reported with TNF-α inhibitors (primarily infliximab and adalimumab), as well as with secukinumab, ustekinumab, and ixekizumab 6
• Patients with prior drug-induced ILD require thorough screening and careful monitoring during biologic treatment 6
• Early detection and precise diagnosis of pulmonary adverse events, especially differentiation from infectious diseases, is essential 6

Common Pitfalls to Avoid

• Do not attribute all respiratory symptoms to obesity or sleep apnea without evaluating for ILD, as 80% of patients with psoriatic arthritis-associated ILD are symptomatic 2
• Do not assume normal chest radiography excludes ILD—HRCT is required for definitive evaluation in high-risk patients 4
• Do not overlook the dramatically increased COPD risk in smokers with psoriatic arthritis (OR 5.56), necessitating aggressive smoking cessation counseling 4
• Do not continue methotrexate without baseline pulmonary assessment in patients with pre-existing lung disease or smoking history 4