## Most Common Site of Initial Involvement in Pemphigus Vulgaris **Key Point:** The oral mucosa is the most common site of initial involvement in pemphigus vulgaris, occurring in 50–90% of patients at presentation. ### Clinical Presentation Pattern **High-Yield:** Pemphigus vulgaris typically follows a predictable pattern of spread: 1. **Oral mucosa first** (50–90% of cases) — painful erosions, difficulty eating, bleeding gums 2. **Face and neck** — follows within weeks to months 3. **Trunk and flexural areas** — progressive involvement 4. **Palms and soles** — rarely involved (resistant to involvement) ### Why Oral Mucosa is Most Common - Thin, non-keratinized epithelium with minimal stratum corneum - High moisture and friction facilitate acantholysis - Constant mechanical trauma from mastication and saliva - Oral lesions are often the presenting complaint, bringing patients to medical attention ### Histopathological Correlation **Clinical Pearl:** The suprabasal acantholysis pattern ("tombstone" appearance) seen in this patient is pathognomonic for pemphigus vulgaris and occurs at the same sites where clinical lesions manifest. ### Differential Site Involvement | Site | Frequency | Characteristics | |------|-----------|------------------| | Oral mucosa | 50–90% (first) | Painful erosions, bleeding | | Face/neck | Common (second) | Follows oral involvement | | Trunk/flexures | Common | Flaccid bullae, erosions | | Palms/soles | Rare | Thick stratum corneum resists involvement | | Scalp | Uncommon | Not typical initial site | **Mnemonic:** **ORAL-FIRST** — **O**ral mucosa is **R**arely spared, **A**lways appears **L**ate in disease course (meaning early in timeline), **F**ollowed by **I**ntegument, **R**arely affecting **S**oles, **T**ypically **H**eads toward trunk. [cite:Robbins 10e Ch 25]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.