Evaluation of the patient’s history guides the neurologist to consider certain areas of the nervous system and certain disorders to explain the patient’s complaints.
Symptoms of neuromuscular conditions include those that arise from disorder of the sensory nerves (for example numbness, tingling or pain) and those that arise from disorder of the nerves going to the muscles or the muscles themselves (for example, weakness, muscle cramps and muscle atrophy).
Principal nerve disorders include inherited conditions (for example Charcot-Marie-Tooth), metabolic disturbances (for example diabetes) and inflammatory conditions (for example Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy).
Disorders of the motor unit include inherited conditions (for example Kennedy disease and spinal muscular atrophy) and degenerative disorders (for example amyotrophic lateral sclerosis or Lou Gehrig’s disease). These conditions lead to degeneration of the nerve cells that activate muscle fibers and can cause trouble with speech, swallowing and limb weakness.
A specialized junction exists where the nerve meets the muscle, the neuromuscular junction. The most common illness that affects this site is myasthenia gravis, an immune mediated disorder that can cause variable weakness, double vision, speech and swallowing troubles.
Primary diseases of the muscle can be inherited (for example muscular dystrophy), inflammatory (for example inclusion body myositis, polymyositis or dermatomyositis) and can sometimes be due to medications (for example statin medications used to treat high cholesterol, which might cause primary muscle injury).
Testing the neuromuscular system typically involves nerve conduction studies and electromyography. Nerve conduction studies are performed by doctors and technicians with specialized training. A small electrical impulse is applied to the skin or to the nerve underlying the skin; recording electrodes placed over the skin monitor the response. The study measures how quickly nerve impulses travel along the course of the nerve and the size or amplitude of the response; these are compared to normal values to help diagnose the nature of the problem. Electromyography is performed by placing a small disposable needle electrode through the skin directly into the muscle. This special electrode measures the electrical activity generated by muscle fibers supplied by individual nerve fibers, and the response is displayed on a computer screen and a loudspeaker. Together, nerve conduction studies and electromyography help distinguish normal function from abnormal function and can help determine whether the problem arises from cells in the spinal cord, the nerve roots, the peripheral nerves or the muscles.
Risk Factors
- Family history
- Medications
- Underlying disease (for example, diabetes)
- Chronic trauma or pressure (for example, carpal tunnel syndrome)
- Acute injury
Symptoms
- Numbness
- Tingling
- Pain
- Unsteadiness
- Weakness
- Progressive muscle wasting
- Difficulty with speech
- Difficulty swallowing
- Double vision
Resources