14. Weakness - Localization of the Problem

	Pattern of weakness	Tone	Bulk	Reflexes	Sensory Loss	Other
Upper Motor Neuron	Pyramidal†	Spastic	Normal	Increased	Varies depending on location of lesion
Anterior Horn Cell	Pyramidal or myotomal	Spastic or normal	Atrophy	Increased or decreased	None	Fascic-ulations
Peripheral Nerve	Distribution of root, plexus or involved nerve(s)	Normal or reduced	Atrophy	Decreased	Prominent
Neuromuscular Junction	Diffuse	Normal	Normal	Normal (myasthenia) or absent (botulism)	None	Ptosis and ophthalmo-paresis
Muscle	Proximal > Distal	Normal	Normal or patterned atrophy	Normal	None

*Adapted from a table created by Dr. Ann Poncelet.

†Pyramidal weakness involves distal > proximal muscles, the extensors > flexors in the arms and flexors > extensors in the legs, and is characterized by slow movements such as slow finger taps and foot taps.