II. Causes: Pathognomonic Lesions
- 
                          Behcet's Disease
                          
- See Oral Ulcer for differential diagnosis
 - Recurrent and numerous Oral Ulcers involving the Soft Palate and oropharynx
 
 - 
                          Crohn's Disease
                          
- Diffuse mucosal swelling, comble-stoning and deep linear ulcers
 - Pathognomonic "snail-track" ulcers known as pyostomatitis vegetans
 
 - 
                          Lichen Planus
                          
- Erosive: Diffuse erythema and painful ulcers (with radiating striae peripherally)
 - Reticular: White lacy striae typically over the Buccal mucosa
 
 - Lupus Erythematosus
 - Pemphigoid (benign mucous membrane)
 - 
                          Pemphigus Vulgaris (Oral Ulcers are the presenting concern in 50-80% of patients)
- See Oral Ulcer for differential diagnosis
 - Diffuse and painful Oral Ulcers may precede skin findings