What is the difference between a dermatomal pattern and a myotomal pattern of symptoms?

• A. Dermatomal refers to sensory changes following a dermatome; myotomal refers to weakness in a specific muscle group innervated by a single nerve root.
• B. Dermatomal is motor weakness; myotomal is sensory.
• C. Dermatomal and myotomal patterns are the same.
• D. Dermatomal follows nerve root distribution; myotomal follows peripheral nerve distribution.

Answer: (A)

The key idea is distinguishing what is being affected and how it maps to the spine. A dermatomal pattern means sensory changes follow a dermatome, the skin area supplied by a single spinal nerve root. This reflects involvement of the sensory (dorsal) root pathways. A myotomal pattern, on the other hand, shows weakness in a muscle group that is innervated by a single nerve root, reflecting involvement of the motor (ventral) root pathways.

So, dermatomal indicates sensory loss along a skin map tied to a nerve root, while myotomal indicates motor weakness in the muscles that the same nerve root innervates. They’re not the same, and the distributions differ: dermatomes are skin territories; myotomes are muscle groups.