What are the appropriate diagnostic tests for suspected generalized pustular psoriasis?

Diagnostic Tests for Suspected Generalized Pustular Psoriasis

The appropriate diagnostic workup for suspected generalized pustular psoriasis (GPP) should include complete blood count, comprehensive metabolic panel with liver and renal function tests, inflammatory markers, skin biopsy, and consideration of genetic testing for IL36RN mutations. 1, 2, 3

Initial Laboratory Evaluation

• Complete Blood Count (CBC) with differential

  • Look for neutrophilia, which is commonly present during GPP flares 2
  • Essential for monitoring disease activity and potential bone marrow suppression from treatments

• Comprehensive Metabolic Panel

  • Liver function tests (AST, ALT, alkaline phosphatase, bilirubin)
  • Renal function tests (BUN, creatinine)
  • Electrolytes with special attention to calcium levels (hypocalcemia is common) 2

• Inflammatory Markers

  • C-reactive protein (CRP) - typically elevated during flares 2
  • Erythrocyte sedimentation rate (ESR)

Confirmatory Testing

• Skin Biopsy

  • Essential for definitive diagnosis
  • Histopathology showing spongiform pustules of Kogoj (collections of neutrophils in the epidermis)
  • Helps differentiate from other pustular conditions 3

• Genetic Testing

  • IL36RN gene mutations (associated with DITRA syndrome)
  • Consider testing for CARD14, AP1S3, MPO, and SERPINA3 mutations 4
  • Particularly important in familial or early-onset cases 5

Additional Testing Based on Clinical Presentation

• Infectious Disease Workup

  • Bacterial cultures of pustules to rule out infectious causes
  • Consider viral studies if clinically indicated

• Hepatitis Panel

  • Hepatitis B and C screening prior to initiating systemic therapy 1

• Tuberculosis Screening

  • Tuberculin skin test or interferon-gamma release assay
  • Essential before starting biologics 1

Pre-Treatment Laboratory Evaluation

Before initiating specific treatments, additional testing may be required:

• For Methotrexate Consideration:

  • Liver function tests
  • Complete blood count
  • Serum creatinine 6, 1

• For Cyclosporine Consideration:

  • Blood pressure measurement
  • Serum creatinine
  • Magnesium, potassium, and uric acid levels 6

• For Retinoids Consideration:

  • Lipid profile
  • Pregnancy test for women of childbearing potential 6, 1

Monitoring During Flares

During acute flares, more frequent monitoring is recommended:

• CBC, CRP, liver and renal function tests every 1-2 days during severe flares
• Electrolytes with particular attention to calcium levels
• Cardiac monitoring if systemic symptoms are severe

Common Pitfalls to Avoid

• Failure to distinguish from other pustular conditions - GPP must be differentiated from acute generalized exanthematous pustulosis, pustular drug eruptions, and other neutrophilic dermatoses 3

• Missing systemic complications - GPP can lead to life-threatening complications including sepsis, renal failure, hepatic failure, respiratory failure, and heart failure 2

• Inadequate pre-treatment screening - Comprehensive baseline testing is essential before initiating systemic therapies to avoid treatment-related complications 1

• Overlooking pregnancy status - Many GPP treatments are contraindicated in pregnancy, requiring careful consideration in women of childbearing potential 6, 1

By following this comprehensive diagnostic approach, clinicians can accurately diagnose GPP, assess disease severity, identify potential complications, and prepare for appropriate treatment initiation.