How is it Diagnosed?
Psoriasis vulgaris, the most common form of psoriasis, is primarily diagnosed through
clinical evaluation. The diagnosis starts with a detailed history, including onset, duration,
triggers (e.g., stress, infections, trauma, medications), and family history. Physical
examination focuses on characteristic lesions: well-demarcated, erythematous plaques
with silvery-white scales, typically found on extensor surfaces such as elbows, knees,
scalp, and lower back.
Dermatologists assess the type, distribution, and extent of lesions. The severity is
quantified using tools like the Psoriasis Area and Severity Index (PASI) or Body Surface
Area (BSA). Nail involvement and signs like pitting or onycholysis support the diagnosis.
In atypical presentations or when confirmation is required, a skin biopsy may be
performed. Histopathology typically reveals hyperkeratosis, parakeratosis, acanthosis,
elongation of rete ridges, and a diminished granular layer with Munro microabscesses.
Laboratory tests are not routinely required for diagnosis but may be used to rule out
differential diagnoses such as eczema, fungal infections, or cutaneous lupus. If systemic
therapy is considered, baseline blood tests including CBC, liver and renal function, and
screening for latent infections (like TB or hepatitis) may be conducted.
Additional imaging is not necessary unless psoriatic arthritis is suspected, in which case
joint X-rays or MRI may help identify inflammatory changes.