Weakness / Paralysis: Clinical Differentiation

Myogenic vs neurogenic weakness

	Myogenic	Neurogenic
Reflexes	Present despite significant weakness	Absent even with mild weakness
Weakness vs wasting	Weakness > wasting	Wasting > weakness
Sensation	Normal	May have sensory changes
Fasciculations	Absent	Present

UMN vs LMN lesions

UMN = above the anterior horn cell in the spinal cord. LMN = at or below the anterior horn cell. A spinal cord lesion produces LMN signs at the level of the lesion and UMN signs below it (see myelopathy).

	UMN	LMN
Weakness	Present	Present
Wasting	Nil (or mild)	Present
Power	Reduced	Reduced
Tone	Increased ± clonus	Decreased
Fasciculations	Absent	Present (sometimes)
Reflexes	Increased	Decreased (or absent)
Plantars	Upgoing	Downgoing