Numbness and tingling are common symptoms of sciatica and nerve root impingement ( also called a pinched nerve in layman's terms.)
Sciatica simply means an irritation of the sciatic nerve
The nervous system is made up of:
In the lumbar spine, as the spinal cord branches, it forms nerve roots which leave the spine, one on each side at each vertebral level . These nerve roots 'bundle together' to form two major peripheral nerves in the legs, the sciatic nerve and the femoral nerve.
The large sciatic nerve runs from your lower back through the buttock area and down the back of your leg and calf. The femoral nerve starts from nerve roots slightly higher up the lumbar spine and runs down the front of your thigh and shin.
The Lumbar Plexus - showing sciatic and femoral nerve origins in the spine
Both the femoral and sciatic nerves are made up of different types of nerve fibres including motor fibres which control muscles and movement, but also importantly, sensory fibres which control feeling.
If the sciatic nerve is irritated, then these sensory fibres can get involved and can't do their job properly. This leads to the changes in feeling that happen with a pinched nerve. Aside from severe pain (which is a very nasty change in feeling) the other very common symptoms of sciatica are numbness and tingling in the feet and legs.
If the nerve is particularly irritated and the motor fibres are involved you can have tingling, numbness and weakness in the legs. Occasionally you also lose a spinal reflex - which is where you are tapped on the knee or ankle to see if they jerk involuntarily. You won't know if there is a change to this, your doctor will test for it.
Where you feel the tingling and numbness in the leg or feet tells us which nerve root irritation you have.
The femoral nerve starts with the nerve roots from L2-L4 (L=Lumbar, so this means from the 2nd to the 4th lumbar level), the sciatic nerve has roots from lower down L4-S3 (S=Sacral). Because they originate in different places where you feel the symptoms of sciatica including numbness and tingling in the legs, tells us roughly which pinched nerve or nerve root impingement you have.
The following chart shows are approximation of the distribution of nerve root pain and numbness, these are called dermatomes in medical terms.
In my clinical experience the most common sciatic nerve symptom is numbness and weakness and pain in the L5-S1 distribution, this is down the back of the leg and into the outside of the foot.
Anything that causes a nerve root irritation can cause sciatica, this is most commonly a lumbar disc bulge or prolapse. Occasionally age changes can cause a narrowing of the amount of space that the nerve root needs when it leaves the spine, this is called foraminal spinal stenosis and it can cause the same symptoms as a disc bulge. You can read more about disc bulges and see a slideshow in this section.
Yes it is, if you have a nerve root irritation there is a good chance you won't have back pain at all. Commonly these symptoms of sciatica start in the limb and can be very confusing. Often my patients will describe an aching or burning toothache that started in their calf or foot, with numbness being one of the key symptoms.
Yes, there are several other problems which can give you these symptoms, so you need to go and see your doctor to make sure you have a diagnosis. The other common causes are peripheral neuropathy, most commonly diabetic peripheral neuropathy, and some other diseases of the nervous system.
Meralgia paresthtica can give you a strange numb patch on your outer thigh.
Lumbar spinal stenosis can cause very similar symptoms.
Cervical myelopathy is a serious condition which can also cause an alteration in how your legs and arms feel.
Firstly go and see your doctor to get a clear diagnosis. Sciatic pain is usually only on one side – if it is in both legs or if you feel saddle numbness ( literally the bit you would feel if you were sitting on a saddle) you need to see your doctor straight away.
Read this page on red flags or serious back problems and if you have any of these symptoms, again go and see a doctor straight away.
I also have some helpful tips for managing the symptoms of sciatica on this home treatment for sciatica page.
Here is is a nice video describing the symptoms of sciatica:
(The paper he is referring to is the one I wrote about on this sciatic nerve pain page.)
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van der Windt DA, Simons E, Riphagen II, Ammendolia C, Verhagen AP, Laslett M, et al. Physical examination for lumbar radiculopathy due to disc herniation in patients with low-back pain. Cochrane Database of Systematic Reviews [Internet]. John Wiley & Sons, Ltd; 1996 [cited 2012 Jul 23]. Available from http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD007431.pub2/abstract