Investigations in Psoriatic Patients
All psoriatic patients require baseline laboratory screening before initiating systemic therapy, with the specific workup determined by disease severity and planned treatment. 1
Initial Clinical Assessment
Perform a thorough skin examination to confirm the diagnosis and identify psoriasis subtypes (plaque, guttate, pustular, erythrodermic, or inverse variants), as the diagnosis relies primarily on morphologic pattern recognition rather than laboratory tests. 2 Biopsy any atypical skin lesions that don't fit classic psoriasis patterns before starting treatment. 1
Assess disease severity using objective measures:
- Body surface area (BSA) involved 1, 3
- Psoriasis Area and Severity Index (PASI) score 1, 4
- Dermatology Life Quality Index (DLQI) for subjective impact 1, 4
Screen for psoriatic arthritis in all patients, as approximately 20% will develop joint involvement. 4 Examine for joint tenderness, swelling, and enthesitis.
Baseline Laboratory Investigations
For patients requiring systemic therapy, obtain the following baseline tests:
Universal Screening (All Systemic Therapies)
- Complete blood count with differential 5, 1
- Liver function tests (AST, ALT, bilirubin, albumin) 5, 1
- Serum creatinine and electrolytes 5, 1
- Hepatitis B and C screening 6
- Pregnancy test in women of childbearing potential 5, 1
Treatment-Specific Additional Tests
For Methotrexate:
- Consider baseline liver biopsy, particularly in patients with risk factors for liver disease 5, 1
- Eye examination for cataracts (theoretical risk exists) 5, 1
- Detailed alcohol use history 6
- Review all medications for hepatotoxic potential and drug interactions 5, 6
For Retinoids (Etretinate/Acitretin):
- Fasting serum lipids 5, 1
- Comprehensive contraception counseling (teratogenic for 2 years post-treatment) 5, 1
For PUVA Phototherapy:
- Eye examination to rule out cataracts 5, 1
- Assessment for history of skin cancer or previous UV/radiation exposure 1
- Minimum phototoxic dose determination at 72 hours 5, 1
For Cyclosporin:
- Baseline blood pressure measurement 5
- Glomerular filtration rate determination 5
- Assessment for malignancy history 5
Comorbidity Screening
Screen all psoriatic patients for cardiovascular and metabolic comorbidities, as psoriasis is associated with significantly increased odds of multiple systemic diseases. 7
Specifically assess for:
- Cardiovascular disease (congestive heart failure OR 1.63, ischemic heart disease OR 1.51) 7
- Diabetes mellitus (uncomplicated OR 1.37, complicated OR 1.32) 7
- Hyperlipidemia (OR 1.28) 7
- Hypertension (OR 1.24) 7
- Obesity and metabolic syndrome 3
- Depression and smoking history 3
- Renal disease (OR 1.45) 7
- Liver disease and viral hepatitis (OR 1.34 for both) 7
Refer patients to internal medicine or primary care for comprehensive evaluation and management of identified comorbidities. 3
Critical Pitfalls to Avoid
Never initiate systemic therapy without pregnancy testing and contraception counseling in women of childbearing potential, as all systemic agents are absolutely contraindicated in pregnancy. 1 For etretinate specifically, contraception must continue for 2 years after stopping treatment. 5
Avoid combining systemic agents due to additive toxicity unless absolutely necessary. 1
Do not rely on laboratory tests alone for diagnosis - psoriasis diagnosis depends on clinical pattern recognition, and blood tests are generally not valuable diagnostic tools. 2
Screen for drug interactions before prescribing methotrexate, particularly NSAIDs, trimethoprim, salicylates, and alcohol, which can precipitate severe toxicity. 5, 8