Lecture by Prof. Osama Shukir Muhammed Amin FRCP(Edin), FRCP(Glasg), FRCP(Ire), FRCP(Lond), FACP, FAHA about the clinical aspects of upper and lower motor neuron lesions.

1. “Clinical Aspects of Upper and
Lower Motor Neuron Lesions”
Osama Shukir Muhammed Amin
MBChB, MD, MRCP, FACP, FAHA, FCCP(USA), FRCP(Edin),
FRCP(Glasg), FRCP(Ire), FRCP(Lond)
Associate Professor of Neurology
School of Medicine, International Medical University,
Malaysia

3. Left corticospinal tract:
Note the origin and journey!

4. Function of the cortico-spinal (pyramidal)
tracts?
The cortico-spinal tract is
involved in the volitional
activity of skeletal
muscle movements of
the contralateral side.
• Upper limbs: shoulder abduction, as well as
elbow, wrist, and fingers extensions.
• Lower limbs: hip and knee flexion, as well as ankle
dorsi-flexion and planter eversion.
Antigravity muscles and
movements?

5. Note:
These movements are further
controlled/modulated by the
extrapyramidal and cerebellar
systems, with respect to initiation,
coordination, speed, tone, etc.

6. Lesion(s) of a cortico-spinal tract?
• This would result in loss of function of that tract with
secondary dominance of extrapyramidal and other
tracts’ functions; e.g., rubrospinal, vestibulospinal,
tectospinal, etc.
• The resulting clinical features depend on the etiology
of the lesion, onset, severity, multiplicity, and
association with other lesions within and outside the
CNS (i.e., peripheral nervous system).

7. Pyramidal system damage would result in…?
• Weakness or paresis of the targeted movement (there is no
complete paralysis). Monoparesis, hemiparesis, or
quadriparesis.
• Reduced control of volitional movements, especially of distal
fine dexterity; e.g., buttoning and unbuttoning.
• Hypertonia of clasp-knife spasticity and “sustained” clonus.
• Exaggerated deep tendon reflexes.
• Extensor planter reflex (Babinski sign), Hoffman sign,
pronator drift, etc.
• No or very minimal atrophy. Disuse atrophy occurs in
longstanding cases.

8. That is to say:
Signs of upper motor
neuron lesion!
And, this reflects what?
Any lesion from the
cerebral cortex down to
the anterior horn cells
of the spinal cord!

9. Is it a “patterned” type of weakness?
YES!
The pattern of pyramidal weakness is weakness of upper
limbs’ extensors and lower limbs’ flexors.
For instance, left-sided pyramidal weakness, grade 3
power in both upper and lower limbs.

10. Note the origin,
course, and target
of lower motor
neurons!

11. Lower motor neuron lesions’ signs?
The classical signs are:
Weakness or complete paralysis.
Hypotonia (flaccidity).
Hyporeflexia or areflexia.
Fasciculation (involuntary rippling muscle
movements).
Early and prominent atrophy.

12. Such signs would reflect what?
Any lesion from the spinal
cord’s ventral horn alpha motor
neurons down to the muscle
fibers (i.e., a long pathway).

13. How would they present clinically?
The presentation depends on the etiology, site of
the lesion, multiplicity of the lesion, onset, and
progression.
And, if there is any coexistent central nervous
system damage.

14. Where, localize?
•Spinal cord anterior ventral horn lesions.
•Radiculopathy.
•Plexopathy.
•Motor-end plate diseases.
•Myopathy/myositis.
PS: Each of them depicts a unique constellation of
symptoms and signs.

15. Rock relief of king Naram-Sin (beloved of moon god Sin), Mountain
Qaradagh, Iraq. Circa 2200 BCE. Photo © Osama S. M. Amin.