Department of Pathology, University of Oklahoma Health Sciences Center

NeuroTest Question #96 Next question Previous question

Answer: The answer is (A) and the followings are true:  Level of difficulty: 4 NeuroTest NeuroLearn NeuroHelp

1. Type I fibers are smaller then type II fibers.

2. Can be seen in demyelinating polyneuropathy.

3. Can be seen in congenital fiber type disproportion.

Discussion: 

• Pathology of the case: The biopsy material was obtained from a 26 year-old woman with the chief complain of muscle weakness. In this particular case, the ATPase reaction is performed at pH 9.4. The type I fibers are pale and type II fibers are large. In general, the type I fibers have roughly about half the diameter of type II fibers. These features are in contrast to disuse atrophy where type II fibers are typically atrophic and smaller then type fibers. Although these histologic features are compatible with congenital fiber type disproportion, this diagnosis is essentially a diagnosis of exclusion. It is quite uncommon for congenital fiber type disproportion to have initial presentation in adults. In addition, other neuromuscular problems such as demyelinating polyneuropathy can also produce this histologic picture. [Click here to see a case of congenital fiber type disproportion]

Comment: KarMing-Fung@ouhsc.edu