There is selective atrophy of Type 2 muscle fibers . In children this degree of type 2 atrophy is common in congenital myasthenia . Numerous fibers have focal or diffuse loss of myosin . The patient probably has severe diffuse weakness and respiratory failure. The syndrome is known as myosin-loss, or acute quadriplegic, myopathy .
Fiber type grouping without fiber atrophy suggests chronic non-progressive denervation.
Strength may be reduced or normal in this muscle.