Spinal Dysfunction, Transcranial Magnetic Stimulation, and Motor Evoked Potentials

Abstract

Since 5 years, this 45-year-old female patient occasionally suffers from a tingling sensation and weakness in her left arm and leg. After some initial improvement, the muscle weakness in her left leg has slowly, but progressively worsened. Her leg is dragging, particularly after she has walked for a while. The leg also feels unstable although sensibility is normal. She currently has no complaints about her right leg or her arms. The neurologist finds that she has normal muscle force in her arms and a slight weakness in her legs (proximal iliopsoas and hamstring muscles MRC 5−). Although she can still walk on her toes and heels and can stand on one leg, hopscotching on her left leg is impossible. Her reflexes are bilaterally normal in her arms, but the knee jerk and Achilles tendon reflexes in her legs are asymmetrically increased (left stronger than right with extinguishing clonus). Her footsole (plantar) reflexes cannot be evoked. These findings indicate that this patient suffers from a slight pyramidal syndrome, which results from damage to or dysfunction of the upper motor neurons. Since these complaints are rather aspecific and can still reflect several diseases, the neurologist decides to initiate further investigations.

Glossary

Anterior horn

Here: frontal grey matter of the spinal cord, containing the alpha motor neurons

Babinski sign

Abnormal plantar (footsole) reflex: upward response of the big toe (dorsiflexion) and spreading of other toes

Capacitor

Electric component consisting of a pair of conductors separated by an insulator; when there is a potential difference across the two conductors, the capacitor can store energy

Clonus

Repetitive relatively large movement resulting from a reflex

Corticocortical

Between two cortical areas

Efferent

Away from the center; e.g. nerve fibers running from the spinal cord to the hand. Opposite to afferent

Fasciculations

See Glossary Chap. 9

Hand knob

Area of the precentral gyrus representing hand motor function, recognizable on MRI by its knob-like shape

Hot spot

Here: area of increased activation in an fMR image

Lipid

Fatty molecule

Motor neuron

See Glossary Chap. 2

MRC

See Glossary Chap. 2

Multiphasic

Here: response curve exhibiting multiple positive and negative peaks

Plexus brachialis

Bundle of nerve fibers, originating from the spine and proceeding through the neck and armpit to the arm

Pyramidal syndrome

The complaints associated with damage to the pyramidal or corticospinal tract (axons originating in the cerebral cortex and running down into the spinal cord); spasticity, muscle weakness, Babinski sign

Rolandic region

Brain area around the central sulcus, separating the frontal and the parietal lobe

Somatotopy

Preservation of relative spatial location throughout the central nervous system (e.g., hand and arm sensory information is processed in adjacent areas in the primary somatosensory cortex)

Spasticity

Increased resistance to passive movement at increasing speed of anti-gravity muscles

Tinnitus

Perception of sound in the ear without an external sound source being present

UPDRS

Unified Parkinson’s disease Rating Scale used for longitudinal assessments of the progression of Parkinson’s disease. The scale incorporates questions related to motor functioning, activities of daily life and mental problems

Vertex

Top of the head, coincident with the EEG position Cz, which is halfway the inion and nasion and the two pre-auricular points (see Glossary Chap. 4)