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: Orthopaedics
13, years old boy, the LEAST common cause of proximal lytic lesion of the head of the femur is - 
Select and explain. 
A. Plasmacytoma, B. Metastasis, C. Histiocytosis, D. Bone tumour
A: Plasmacytoma
Answer: A: Plasmacytoma 
Explanation: If multiple myeloma occurs as a solitary lesion it is known as Plasmacytoma
Age gp is 6th-7th decade, Rare before 40yrs of age
So the lytic lesion in a 13 yrs old boy cannot be a plasmacytoma