A disorder affecting a lower motor neuron (LMN) presents with a number of clinical findings.
Clinical features of a lesion affecting a lower motor neuron:
(1) weakness (loss of muscle strength)
(2) muscle loss with atrophy
(3) hypotonic or flaccid muscle
(4) muscle cramps
(5) hyporeflexia
(6) muscle fasciculations
If the injury is unilateral, then the affected side may be compared to the uninvolved side.
Electromyography (EMG) and nerve conduction studies show:
(1) a decrease in the muscle action potential following a supramaximal electrical stimulation.
(2) a decrease in motor neuron conduction velocity
(3) a normal sensory nerve conduction velocity (in a pure LMN disorder)
