Dominic Stone
Muscle cramps are sudden, painful, involuntary contractions of a muscle or group of muscles. While muscle cramps are common and often benign, they can sometimes be a symptom of nervous system malfunction. Neuropathy, a disorder that prevents nerves from functioning properly, can cause muscle cramps. In some cases, neuropathy is caused by heredity, vitamin deficiency, infection, and kidney disease. Certain medications can also cause muscle cramps. Nerve conduction studies and needle electromyography (EMG) can be used to differentiate neurogenic from myogenic cramps.
| Characteristics | Values |
|---|---|
| Muscle cramps | A sudden, brief, unintended (involuntary), and usually painful contraction of a muscle or group of muscles |
| Muscle cramps occurrence | During or after vigorous exercise or during rest |
| Muscle cramps occurrence in sleep | Affects calf and foot muscles, causing the foot and toes to curl downward |
| Muscle cramps occurrence in sleep | Affects approximately 37% of the population in America over 60 years of age |
| Muscle cramps occurrence in sleep | Predisposing factors include neurological disorders, hormonal and metabolic disorders, and compression of nerve roots or compressed arterial vessels |
| Muscle cramps occurrence in sleep | Stretching the affected muscle often relieves the cramp |
| Muscle cramps occurrence in people with chronic renal failure undergoing dialysis | Up to 50%, especially involving the lower limbs |
| Muscle cramps occurrence in people with endocrine disorders | Affect electrolyte levels (eg, Ca2+ or PO4+) |
| Muscle cramps occurrence due to medication | Thiazide diuretics, statins, beta-agonists, acetylcholinesterase inhibitors, cimetidine, steroids, morphine, penicillamine, some immunosuppressants, cardiotropics, antiretrovirals, and psychotropic medications |
| Muscle cramps occurrence due to nerve issues | Nerve conduction studies and needle EMG can be helpful in differentiating neurogenic from myogenic cramps |
| Muscle cramps occurrence due to nerve issues | Serum creatine kinase (CK) levels may be elevated in myopathy |
| Muscle cramps occurrence due to nerve issues | Repetitive peripheral nerve stimulation on conduction nerve studies may show “after-discharges” in cramp-fasciculation syndrome and Isaac’s syndrome |
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What You'll Learn
Neuropathy and nerve damage
Neuropathy is a nerve condition that can lead to pain, numbness, weakness, or tingling in one or more parts of the body. Peripheral neuropathy is a common type of nerve damage that may be caused by underlying conditions, such as diabetes, vitamin deficiency, infection, and kidney disease. It is often associated with diabetes, where high blood sugar levels can cause temporary or permanent damage to nerve tissue. Peripheral neuropathy can also be a side effect of cancer treatment, specifically chemotherapy. This type of nerve damage affects the nerves in the outer parts of the body, such as the feet, legs, hands, and arms.
The peripheral nervous system is made up of sensory nerves that carry information about the environment, and motor nerves that carry bioelectrical information to muscles, resulting in contraction and movement. Neuropathy prevents nerves from functioning properly, and in some cases, it can cause paralysis if a nerve is completely lacerated. However, total paralysis is rare.
The symptoms of peripheral neuropathy depend on which nerves are affected. It can cause abnormal sensations in the affected body area, such as pain, numbness, and tingling. In some cases, it can also lead to a loss of sensation, which can increase the risk of foot problems and infections. If left untreated, peripheral neuropathy can lead to serious complications, such as foot ulcers that can progress to gangrene and may require amputation.
The diagnosis and treatment of peripheral neuropathy depend on the underlying cause. Doctors will typically take a full medical history and perform a physical and neurological examination. Tests such as nerve conduction studies, blood tests, MRI scans, or ultrasound scans may also be done to help identify the cause. Treatment options may include medications, vitamin supplements, physical therapy, or surgery. However, it is important to note that peripheral neuropathy may not always be curable, and managing the condition may involve controlling the underlying chronic condition.
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Neurogenic vs myogenic cramps
Muscle cramps are typically regarded as benign muscle overactivity in healthy individuals. They are sudden, brief, involuntary, and usually painful contractions of a muscle or group of muscles. While muscle cramps are common and often benign, they can occasionally be a symptom of nervous system malfunction.
Neurogenic cramps are caused by nerve dysfunction, while myogenic cramps are caused by muscle dysfunction. Neurogenic cramps are sustained, painful contractions of muscles that are prevalent in patients with and without medical conditions. Investigations are directed toward identifying physiological triggers or medical conditions that predispose patients to cramps. Mechanical disruption, ephaptic transmission, disruption of sensory afferents, and persistent inward currents have been implicated in the pathogenesis of neurogenic cramps.
Myogenic cramps, on the other hand, are caused by issues with the muscle itself rather than the nerves. Myopathy, or muscle disease, can cause myogenic cramps. Serum creatine kinase (CK) levels may be helpful in differentiating myogenic cramps, as CK levels are often elevated in myopathy. However, it is important to note that CK levels can also be mildly elevated in neurogenic processes.
It is important to distinguish between neurogenic and myogenic cramps because each has unique pathophysiology and management. Doctors will typically perform a physical examination, including a neurological examination, to assess muscles and reflexes. If cramping is widespread, doctors may measure blood sugar and electrolyte levels and perform blood tests to check for kidney malfunction. If muscle weakness is widespread and suspected to be related to a nervous system problem, magnetic resonance imaging (MRI) of the brain and spinal cord may be performed.
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Nerve conduction studies
A nerve conduction velocity (NCV) test measures how fast an electrical impulse moves through a nerve. The test can identify nerve damage and is often used to diagnose carpal tunnel syndrome and other peripheral nerve disorders. During the test, the nerve is stimulated with a very mild electrical impulse, and the resulting electrical activity is recorded by another electrode. The speed is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between them.
A nerve conduction study can be performed in an outpatient setting or as part of a hospital stay, depending on the situation. The test may take from 15 minutes to over an hour, depending on how many nerves and muscles are tested. The number of nerves tested depends on the patient's case and what the provider is looking for. The patient should wear comfortable, loose-fitting clothing and avoid creams, lotions, or perfumes on their skin before the test, as these can affect accuracy.
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Motor nerve issues
Motor nerves carry bioelectrical information to muscles, resulting in contraction and movement. When a muscle cramp occurs, the muscle experiences involuntary contraction and is usually painful. Although muscle cramps are common and often benign, they can sometimes be a symptom of nervous system malfunction. Nocturnal cramps, or muscle cramps at night, tend to become more common with increasing age. However, it is not completely understood why motor nerves might suddenly start firing when the leg is relaxed during sleep.
Neuropathy is a disorder that prevents nerves from functioning properly and can cause paralysis if a nerve is completely lacerated. It can be caused by heredity, vitamin deficiency, infection, or kidney disease. In the case of neuropathy, controlling the chronic condition can play a key role in managing it, and it may be relieved by medications, vitamin supplements, physical or occupational therapy, splinting, or surgery.
Nerve conduction studies and needle electromyography (EMG) can be used to differentiate neurogenic from myogenic cramps. Doctors may also measure blood sugar and electrolyte levels and perform blood tests to check for kidney malfunction, which can cause abnormal levels of calcium and magnesium. If the cramped muscles are weak, an EMG test can be performed by inserting a small needle into the muscle to record electrical activity during rest and contraction.
In some cases, muscle cramps may be caused by involuntary nerve discharges or a lack of blood flow to the leg muscle. Dehydration and electrolyte imbalances can also contribute to muscle cramps. Additionally, certain medications, endocrine disorders, and neurologic conditions affecting the peripheral nerve can increase the risk of muscle cramps.
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Neurologic examinations
Muscle cramps are a sudden, brief, unintended, and usually painful contraction of a muscle or group of muscles. Although they are common and often benign, they can sometimes be a symptom of nervous system malfunction.
If the cramping is widespread and reflexes are overactive, doctors may measure blood sugar and electrolyte levels, including calcium and magnesium. Blood tests can also be performed to check for kidney malfunction, which can cause abnormal levels of these electrolytes. If the cramped muscles are weak, electromyography (EMG) may be performed. This involves inserting a small needle into the muscle to record its electrical activity at rest and during contraction.
If muscle weakness is widespread and suspected to be related to a nervous system issue, magnetic resonance imaging (MRI) of the brain and spinal cord may be conducted. This can help identify any disorders causing the muscle cramps, which can then be treated.
In addition to these tests, a nerve conduction study can be used to measure how quickly nerves carry electrical signals, which can be useful in diagnosing carpal tunnel syndrome and other peripheral nerve disorders. In some cases, a nerve biopsy may be recommended to examine a small portion of the nerve for any abnormalities.
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