Carpal tunnel syndrome is a very common reason for requesting an electromyogram, in Paris and elsewhere. It is a common and benign condition, provided it is identified and treated early.
Initial Symptoms
In the vast majority of cases, the onset is gradual. The first symptoms are often paresthesias—tingling sensations in the hand, occurring at night or in the morning, which subside upon changing the position of the arm or hand. These paresthesias typically affect the thumb, index finger, middle finger, and half of the ring finger.
Symptoms may also occur during the day, during manual activities (using the phone, driving, repetitive tasks...).
Many patients report a feeling of hand clumsiness, weakness, or fatigue, particularly when holding objects.
Signs of Worsening
Without treatment, the condition may progress gradually.
The paresthesias then become increasingly frequent and persistent, eventually becoming permanent and accompanied by a loss of sensation in part of the hand. This loss of sensation can feel like permanent numbness.
Another sign of worsening is a loss of muscle strength, particularly in the muscles that control thumb opposition, leading to weakness in the pinch grip and difficulty holding objects, or opening bottles and jars.
Some patients describe pain in the wrist and hand, characterised by crushing, pressure, or electric shock-like sensations.
In the most advanced forms, muscle wasting occurs at the base of the thumb, known as thenar atrophy.
The Origin of this Syndrome
Carpal tunnel syndrome is what is known as an entrapment neuropathy, meaning the compression of a nerve within a narrow anatomical space. Here, the median nerve is compressed within the carpal tunnel at wrist level. This tunnel is a rigid, non-yielding space containing the median nerve and the flexor tendons of the fingers.
Any increase in pressure within this tunnel (due to inflammation, tissue thickening, fluid retention, or repetitive movements) results in compression of the median nerve.
Initially, this causes functional impairment due to a focal and reversible alteration of the nerve's myelin sheath. In more advanced stages, structural damage to the nerve develops (axonal degeneration or loss).
What is the Cause?
Several contributing factors have been identified:
- Manual activities, repetitive movements, and mechanical strain on the wrist.
- Pregnancy, due to fluid retention.
- Associated conditions (diabetes, thyroid disorders, obesity, other neuropathies...).
It is not uncommon for patients to present with none of these contributing factors.
How is it Diagnosed?
The diagnosis is primarily clinical, based on symptoms and their location.
Several investigations or tests help confirm or refine the diagnosis:
- Clinical examination, by reproducing symptoms when the doctor taps over the carpal tunnel or during sustained wrist flexion.
- Electromyography (EMG), the gold standard investigation. It confirms the diagnosis, assesses severity, detects signs of structural nerve damage, and rules out other causes (such as cervical nerve root compression or other neuropathies).
- Ultrasound or MRI are useful in cases of diagnostic uncertainty or atypical forms, allowing for the evaluation of the morphological features of the median nerve and its surrounding environment within the carpal tunnel.
Treatments
Treatment depends on the severity of the symptoms, the duration of progression, signs of severity, and the clinical context (pregnancy, manual activity, wrist trauma...).
Conservative treatment is recommended at early stages for mild to moderate forms.
- Night wrist splinting. This involves keeping the wrist in a neutral position throughout sleep to reduce pressure within the carpal tunnel.
- Local corticosteroid injection into the carpal tunnel. The anti-inflammatory effect can provide rapid, though often temporary, relief.
Surgical treatment is recommended if conservative treatment fails, or in severe cases. Conceptually, the procedure involves releasing the carpal ligament to relieve pressure on the median nerve.
In rare cases, the physician may advise observation without immediate treatment, waiting for spontaneous improvement (such as when symptoms arise during pregnancy or temporary, unaccustomed manual work).
Why undergo an EMG?
In the context of carpal tunnel syndrome, an EMG serves several purposes.
It enables:
- Reliable and objective assessment of median nerve conduction.
- Confirmation of the diagnosis.
- Evaluation of nerve damage severity, looking for indicators of severity such as axonal loss or denervation.
- Screening for other neuropathies.
Consequently, the EMG directly guides the therapeutic strategy.
In Summary
Carpal tunnel syndrome is a compression of the median nerve at the wrist
The first symptoms are nocturnal tingling in the hand and fingers
Progression is often gradual
Signs of severity may develop (loss of sensation, weakness)
The EMG is the key investigation
Treatments are effective, and recovery is optimal when treatment is initiated early
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