This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of Muscle and Muscular Dystrophies, Subject name: Pediatrics
10 years old Ramu has increasing muscle weakness and raised CPK levels. The most likely defect is in plasma membrane of- 
Select and explain. 
A. Nerves, B. Muscle fibres, C. Basement membrane, D. All body cells
B: Muscle fibres
Answer: B: Muscle fibres 
Explanation: Ans. is 'b' Muscle fibres (Ref. Chandrasoma Taylor, 3/e, p. 953).Increase in CPK level with muscle weakness suggests muscle cell damage.Creatine kinase is an enzyme found mainly in:Skeletal muscle*Heart*Brain*Its levels will be raised in the serum when any of the above mentioned cell is damaged.There are various isotypes of the enzyme which are specific for difference cells.Enzyme - TissueCreatine kinase - Heart*(MB isoenzyme)Creatine kinase - Brain*(BB isoenzyme)Creatine kinase - Skeletal muscle*(MM isoenzyme)Other enzymes elevated in muscle diseasesAldolase*Aminotransferases specially (ACT) *Lactate dehydrogenase*