A
 Myosin ATPase, pH 9.4 |
Image: There is selective atrophy of Type 2 muscle fibers. What is the differential diagnosis in adults (Left)? Answer: Disuse, Aging, Weight loss, Systemic disease & Paraneoplastic disorders What is the differential diagnosis in children (Right)? Answer: Severe type 2 atrophy is common in congenital myasthenia. |
B ATPase, pH 9.4 |
Image: All the muscle fibers in this biopsy are type I. What is the differential diagnosis? Answer Central core Large fiber type grouping Demyelinating neuropathies |
C
 ATPase pH 9.4 stain |
What is the fiber type abnormality? What is the differential diagnosis? Image: Type I muscle fibers are selectively small, Answer: Very small type I muscle fibers are common in congenital myopathies such as Centronuclear Nemaline rod Fiber type disproportion, congenital. Rigid spine syndromes NOTE: Type 2 muscle fibers can be selectively enlarged with exercise. |
D Myosin ATPase, pH 9.4 stain |
What is wrong with the pattern of ATPase staining? Answer: Some muscle fibers have focal or diffuse loss of myosin. Some muscle fibers have staining that is less intense than Type I fibers. Some muscle fiber have a focal loss of myosin staining. What are likely clinical features in this patient? Answer: Severe proximal > distal weakness and respiratory failure. The syndrome is variously called Myosin-loss, Acute quadriplegic, ot Critical illness myopathy. |
E ATPase pH 9.4 stain |
Describe the pattern of ATPase staining of muscle fibers. Answer: Fiber type grouping without muscle fiber atrophy There was denervation and reinnervation of the muscle in the past What does this pattern of ATPase staining suggest about the disease course? Answer: Non-progressive course; Strength may be reduced or normal in this muscle. |