If someone mentions that you have a pinched nerve, they are likely talking about a radiculopathy. Radiculopathy can be caused by conditions such as disc herniations and can lead to sciatica pain.
Why is it called a pinched nerve?
Pinched nerve suggests that something is actively squeezing hard on your nerve, but that is not the case. A pinched nerve refers to a phenomenon where something is putting pressure on the nerve. The pressure can be intense or just merely a gentle touch. The pressure can come from disc herniations, tumours, bony growth (e.g., bone spurs), or even inflammation.
Symptoms of a pinched nerve
Many people associate pinched nerve with intense pain. However, that does not have to be the case. In fact, having neurological symptoms in the absence of pain is the most definitive sign that you have a pinched nerve.
A pinched nerve often presents with the following symptoms
- Numbness
- Tingling or “pins and needles” (i.e. paresthesia)
- Sharp or burning pain
- Deep, dull aches
- Electric shock sensation
- Muscle weakness
How is a pinched nerve assess?
Pinched nerve can be assessed during a physical examination. A light touch test can be conducted to see if a patient is still able to perceive gentle contacts. This test can be performed with a cotton ball. A clinician such as a chiropractor will perform the test on the skin following each dermatome to ascertain which nerve root is affected.
Other tests that can be used to assess sensory changes include pinprick or sharp/dull test, as well as sense of vibration test.
Muscle power may also be assessed to determine any motor deficits. Movements will be tested according to each myotome to ascertained which nerve root is affected.
Each myotome is tested then graded 1 to 5:
0 = total paralysis.
1 = palpable or visible contraction.
2 = active movement, full range of motion (ROM) with gravity eliminated.
3 = active movement, full ROM against gravity.
4 = active movement, full ROM against gravity and moderate resistance in a muscle specific position.
5 = (normal) active movement, full ROM against gravity and full resistance in a muscle specific position expected from an otherwise unimpaired person.
Further investigations for pinched nerve
Further investigations such as MRIs and nerve conduction study can identify the location and also severity of nerve compressions.
X-rays
In Singapore, X-rays are often performed first because they are cheap and quick to perform. X-rays is useful for visualising hard structures such as bone. With X-rays, you will be able to see if the nerve compression is the result of issues such as osteoarthritis or bone spurs. It is also possible to identify some tumours with X-ray.
However, X-rays are not useful for visualising soft tissues. You will not be able to see your nerves or spinal discs on X-rays. Sometimes, doctors will assume certain conditions based on X-rays findings. While this may work as a general rule of thumb, it is not always accurate.
How X-rays can show spinal discs issue even though we can’t clearly see spinal discs themselves on X-rays
Personally, I have done an X-ray of my lumbar spine previously. From the X-ray, it is clear there is a reduction in one of my spinal discs height. Although we are not able to visualise the disc, we can see the bones (i.e., vertebrae) at the top and the bottom of each disc. When the bones are closer together, we assume that there is a loss of disc height in the disc. Even though we cannot actually see the disc.
From there, it was assumed that I likely have a disc herniation at that level. In other words, the doctor assumed that my disc height was lower because my spinal disc was being “squeeze” out, into a disc herniation.
Interesting, in the MRI that followed later, there was no disc herniation at the level where I have a reduction in spinal disc height.
MRI (Magnetic Resonance Imaging)
Because X-rays have their limitations, sometimes an MRI is necessary. They are often performed so we can visualise the soft tissues such as intervertebral discs, nerves.
For my case, my MRI was able to show that there was impingement of the L5 nerve root. Not only that, the radiologist was able to see the nerve root was “closely abutted” by one of my disc bulges.
MRI with contrast
Besides your usual MRIs, there is also contrast MRI. This is not commonly performed for impinged nerves but more for spinal cord compression (i.e., myelopathy). When the spinal cord is compressed, you can get neurological symptoms that are very similar to those experienced by patients with a (less serious) spinal nerve impingement.
A MRI with contrast is more invasive than a usual MRI. The contrast is administered either orally or through an intravenous (IV) line. The most commonly used contrast is gadolinium-based contrast agents (GBCAs).
The resultant images is more detailed and helps with decipherability of disease or abnormality inside your body.
Nerve conduction studies
Moving away from imaging, nerve conduction studies (NCS) can also be done. A nerve conduction study is a non-invasive test that measures the speed and strength of electrical signals as they travel through your nerves. You can think of it like a performance test for your nerves – just as we might test the performance of a muscle or joint, we do the same for the nerves, but using electrical impulses.
The test is particularly useful when a nerve is being pinched because it helps us determine whether the nerve is being compressed or irritated. When a nerve is pinched, it can become sluggish or weak, and a nerve conduction study can give us detailed information about the damage.
Selective nerve root block
Selective nerve root block (SNRB) does sound like a common procedure though I do not personally know anyone who has done it as a diagnostic test. SNRB is highly specific because it allows a clinician to test a specific nerve, and to determine if that is the source of the patient’s pain experience.
During this test, an anesthetic or anesthetic with steroid is injected near a spinal root just as it exits the spinal column. The medication works by reducing inflammation and numbing the pain transmitted by the nerve. So, if the source of the pain is coming from the specific nerve, the patient should feel a significant relief.
If no relief is felt, then it is unlikely that a patient’s pain is coming from the nerve.
What are the most common causes of a pinched nerve?
The most common causes of a pinched nerve include disc herniations, bone spurs, spinal stenosis, spondylolisthesis, osteoarthritis, and tumours.
Disc herniations
Disc herniations, also known as slipped disc, occurs when a disc in the spine bulges out of its normal position. The spine is made up of a series of bones called vertebrae that are separated by discs, which act as cushions between the vertebrae. The discs are made up of a tough outer layer called the annulus fibrosus and a soft, gel-like center called the nucleus pulposus.
The cause of disc herniations is likely because of a weakening of the annulus fibres, which allows the inside spongy nucleus pulposus to push its way through. It is not entirely clear why this happens.
Based on current research, age is a predictor of disc herniations. Surprisingly, research does not support that heavy lifting or strength tranning causes disc herniation.
Bone spurs
Bone spurs are also known as osteophytes. They are bony outgrowth from an existing bone. On their own, they are benign and does not cause any issues. However, sometimes bony spurs can protrude into surrounding tissues or foreamens (i.e., open spaces) and can be problematic.
For example, bone spurs can grow into intervertebral foramen. This foramen is also the space where our spinal nerves exit the spinal column. When this space is sufficiently encroached by the bony growth, a nerve impingement can occur.
Outside of the spine, bone spurs are also commonly found in the calcaneus or heel bone. They can cause pain during standing or walking when they exert pressure into surrounding soft tissues.
Bone spurs is a sign of osteoarthritis.
Spondylolisthesis
Spondylolisthesis is a condition where one of the vertebra shifts forwards or backwards from its usual place. When this happens, nerves can be impinged as the intervertebral foramen becomes smaller.
Spondylolisthesis affects between 4-8% of the general population so it’s considered quite common. Most cases of spondylolisthesis are mild and can even be asymptomatic.
Tumours
Tumors can cause nerve impingement by directly pressing on nerve roots, the spinal cord, or surrounding structures. As a tumor grows, it may invade nearby tissues or occupy space in the spine, leading to compression of the nerves, which can result in pain, numbness, tingling, or weakness.
Whether benign or malignant, tumors can disrupt normal nerve function by causing direct pressure or altering the anatomy of the affected area.
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