Among patients with psoriasis, which is the most common site of involvement?

Explanation

## Most Common Site of Psoriasis: Extensor Surfaces **Key Point:** The extensor surfaces of the elbows and knees are the most frequently affected sites in psoriasis, present in up to 90% of patients with plaque psoriasis. ### Anatomical Distribution Pattern in Psoriasis 1. **Extensor Surfaces (Most Common)** - Elbows and knees: ~90% of plaque psoriasis cases - Shins and forearms: frequently involved - Reason: Trauma-prone areas (Koebner phenomenon) 2. **Scalp** - Involved in 50% of psoriasis patients - May be the sole site in some cases - Often misdiagnosed as seborrheic dermatitis 3. **Sacrum and Lower Back** - Common site of involvement - Often overlooked on initial examination 4. **Palms and Soles** - Involved in 10–15% of patients - Pustular variant (pustulosis palmoplantaris) is distinct - Hyperkeratotic plaques with painful fissuring 5. **Intertriginous Areas (Inverse Psoriasis)** - Axillae, groin, inframammary folds - Smooth plaques without scale - Only 3–7% of total psoriasis cases 6. **Face and Neck** - Relatively spared in classic plaque psoriasis - When involved, often sebopsoriasis (overlap with seborrheic dermatitis) ### Frequency Table by Site | Site | Frequency in Plaque Psoriasis | |------|-------------------------------| | Elbows and knees | ~90% | | Scalp | ~50% | | Sacrum/lower back | ~40% | | Palms and soles | 10–15% | | Intertriginous areas | 3–7% | | Face | <5% | **High-Yield:** "Extensor surfaces" is the single most important phrase for NEET PG psoriasis questions. If you see elbows, knees, shins, or forearms in the stem, think plaque psoriasis. **Clinical Pearl:** The Koebner phenomenon (lesions appearing at sites of trauma) explains why extensor surfaces are preferentially affected — they are subject to repeated minor trauma from friction and pressure. **Mnemonic: ELBOWS & KNEES** — The classic "extensor surface" sites that are affected in >90% of plaque psoriasis cases.