What is muscle weakness?
Muscle weakness (or motor deficit) refers to a reduction in the strength of one or more muscles, independent of general fatigue. It can manifest in highly variable ways: difficulty climbing stairs or rising from a chair, arms that tire quickly when raised, drooping eyelids, gait impairment, clumsiness in the hands, or even difficulty swallowing, speaking, or breathing.
When unexplained, progressive, or associated with other neurological symptoms, muscle weakness warrants a rigorous neurophysiological assessment. The key objective is to identify its precise origin to guide treatment as early as possible.
Where is the anomaly located?
Muscle strength depends on a chain of command extending from the brain to the muscle fibre itself. A failure at any level of this chain can cause weakness. The primary objective of the neurological assessment is to locate the affected link.
Causes of central origin, involving the brain or spinal cord, relate to the central nervous system (CNS). Multiple sclerosis, tumours, stroke, myelitis, or spinal cord compression can generate a motor deficit by affecting the pathways descending to the muscles. In these situations, the reference investigations are motor evoked potentials (MEP) and somatosensory evoked potentials (SSEP), which evaluate the integrity of the central motor and sensory pathways respectively.
Causes of peripheral origin (nerves, roots, neuromuscular junction, or the muscle itself) constitute the core of our work at IENA Neurophysiologie. It is this area that the electromyogram (EMG) explores with precision, and where our expertise is fully realised.
Peripheral causes of muscle weakness
Peripheral motor neuropathies
Damage to peripheral nerves can affect their motor fibres and cause weakness in the area supplied by the affected nerve. Neuropathies can be inflammatory (Guillain-Barré syndrome, multifocal motor neuropathy), toxic, hereditary (Charcot-Marie-Tooth disease), or metabolic. An EMG helps specify the mechanism—axonal damage or demyelination—and estimate its severity.
Radiculopathies
Compression of a nerve root by a herniated disc or severe osteoarthritis can lead to weakness in the corresponding muscle group. For example, a lumbar herniated disc compressing the L5 root will cause weakness in foot dorsiflexion and difficulty walking on heels; a C7 cervical issue will affect triceps strength. An EMG identifies the affected root and assesses the extent of muscle denervation.
Amyotrophic Lateral Sclerosis (ALS)
ALS is a condition that simultaneously affects both central and peripheral motor neurones. It manifests as progressive and irreversible weakness, muscle twitching (fasciculations), and muscle wasting (amyotrophy). EMG plays a central role in its diagnosis by demonstrating signs of diffuse denervation across several muscle areas.
Neuromuscular junction disorders
Myasthenia gravis and Lambert-Eaton syndrome are autoimmune diseases that disrupt signal transmission between nerve and muscle. The weakness they cause has an important clinical characteristic: it is variable, fluctuating, and often worsened by exertion in myasthenia gravis, or conversely, improved by exertion in Lambert-Eaton syndrome. EMG with repetitive nerve stimulation and the study of the neuromuscular junction allow these to be objectively demonstrated.
Myopathies
Primary muscle diseases (muscular dystrophies, inflammatory myopathies, polymyositis, dermatomyositis, metabolic or congenital myopathies) cause a weakness of progressive onset, which is often symmetrical and can predominantly affect the limb girdles (shoulders, hips). Needle myography detects specific electrical anomalies in muscle fibres and guides toward a biopsy or genetic testing.
What does the assessment at IENA Neurophysiologie involve?
At IENA Neurophysiologie, we specialise in the investigation of the peripheral nervous and neuromuscular systems. The assessment of muscle weakness is tailored to each patient based on clinical indications.
The electromyogram (EMG) is the pivotal examination. It explores the peripheral nerves by studying their conduction, and the muscles using needle myography. It distinguishes between neurogenic and myogenic disorders, identifies the distribution of the impairment, and clarifies its mechanism.
Motor evoked potentials (MEPs) explore central motor pathways, from the cerebral cortex to the muscles, by stimulating the motor cortex using a painless magnetic field. They are indicated when spinal cord or brain involvement is suspected (multiple sclerosis, spinal cord compression, ALS) and complement the EMG to provide a comprehensive neurophysiological profile.
Somatosensory evoked potentials (SSEPs) explore central sensory pathways in parallel. They are useful when weakness is accompanied by sensory disturbances or when documenting central involvement is required.
The neuromuscular consultation is the clinical stage that precedes or accompanies these examinations. It allows for a detailed history of the condition, a segment-by-segment assessment of muscle strength, a search for associated central or peripheral signs, and the coordination of the diagnostic workup.
When should you seek medical advice?
Consult your physician or seek a neurological opinion if you experience:
Weakness in one or more limbs, of progressive or sudden onset
Difficulty climbing stairs, rising from a chair, or lifting your arms
Abnormally rapid muscle fatigue on exertion, which recovers with rest
Fasciculations (minor, involuntary muscle twitches visible under the skin)
Amyotrophy (muscle wasting) in a limb or segment of a limb
Drooping eyelids, or difficulty swallowing or articulating words
Weakness associated with numbness or pain
Persistent shortness of breath following normal cardiology and pulmonology assessments.
In summary
Unexplained muscle weakness can arise from the central nervous system (brain, spinal cord) or the peripheral nervous system (nerves, neuromuscular junction, muscle)
At IENA Neurophysiologie, we specialise in the exploration of the peripheral nervous system: neuropathies, radiculopathies, myasthenia gravis, ALS, and myopathies
EMG is the first-line examination to locate and characterise neuromuscular impairment
MEPs and SSEPs complete the assessment when involvement of the central motor or sensory pathways is suspected
The neuromuscular consultation coordinates the overall workup and directs you to the appropriate additional examinations
All our examinations are performed by referral (on prescription), with the medical report provided immediately
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Book an appointment for a muscle weakness assessment at IENA Paris 16th
By telephone on 01.89.74.47.69 or via Doctolib
Learn more about the examinations performed at IENA Neurophysiologie