This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
All of the following are primary cutaneous disorder except - 
Select and explain. 
A. Psoriasis, B. Reiter's disease, C. Lichen planus, D. Icthiosis
B: Reiter's disease
Answer: B: Reiter's disease 
Explanation: Reiter's syndrome is primarily a reactive polyarthritis. Cutaneous involvement is a secondary feature.