Nerve testing for foot pain: what to expect

Why testing is used, and why it isn’t always needed

Nerve pain in the foot can come from a nerve trapped in the foot, from the lower back, or from a body-wide condition such as diabetes. Testing can help sort out which. But no single test is perfect, and for many nerve entrapments the examination is the most informative step. A test result is always read alongside your symptoms and what we find on examination.

The examination

The examination is a test in its own right, and it does not require equipment.

• Sensation: light touch and pinprick, a fine nylon filament, and a vibrating tuning fork to map any numb or over-sensitive areas.
• Tapping over the nerve (the Tinel test), which can send tingling into the foot when a nerve is irritated.
• Strength and reflexes in the foot, ankle and leg.
• Squeezing or pressing between the toes, behind the inner ankle or over other common trouble spots.
• Alignment, footwear and gait, which can put a nerve under pressure.
• Circulation, by checking pulses and skin, since poor blood flow can also cause numbness and burning.

Many nerve conditions can be recognized from this alone. For example, an examination is a major part of diagnosing Morton’s neuroma.^[4]

Nerve conduction studies and EMG

Nerve conduction studies (NCS) use small, brief electrical pulses through stickers on the skin to measure how quickly and how strongly a nerve carries signals. Electromyography (EMG) uses a very fine needle placed in a muscle to record its electrical activity. Together they are called electrodiagnostic tests. They are usually performed by a neurologist or a physiatrist (a rehabilitation physician), and we coordinate the testing when it’s needed.

What they can do. They can show whether a nerve is affected, where along its path the problem sits, how severe the damage is, and, in some cases, how likely the nerve is to recover.^[5,6] They are especially useful for telling a pinched nerve in the foot from a nerve-root problem in the lower back, and for identifying a body-wide neuropathy.^[7,5]

What they can’t do. A normal result does not rule out a nerve problem. In an evidence review of tarsal tunnel syndrome, nerve conduction studies were abnormal in some people with the condition, sensory studies were more likely to be abnormal than motor studies, and the actual sensitivity and specificity could not be determined.^[1] Another study noted that the sensitivity of electrodiagnostic testing for tarsal tunnel syndrome is just over 50%. In that study, people with normal and abnormal test results improved by similar amounts after tarsal tunnel release, so a normal test did not mean surgery was less likely to help.^[2] Guidelines for testing entrapment neuropathies in the foot are also limited.^[8]

What to expect. The tests are done in an outpatient setting. The pulses feel like brief tingles or taps, and the needle part can be uncomfortable for a moment. Tell the testing office about the medicines you take, especially blood thinners, and any implanted devices.

Imaging

• X-rays show bones, joints, spurs and alignment.
• Ultrasound uses sound waves to show soft tissues in real time. Findings of nerve entrapment can include a swollen, darker-looking nerve or a change in the nerve’s width, and an examiner can press on the exact spot.^[3]
• MRI shows soft tissue in fine detail and can reveal a cyst, a mass, a swollen tendon sheath or changes around a nerve.^[3]

For Morton’s neuroma, a pooled analysis found ultrasound and MRI about equally sensitive for finding the neuroma.^[9] Imaging of the lower back, such as an MRI of the lumbar spine, is used when the back may be the source. Scans are always read together with the examination, because abnormalities can appear in people with no symptoms.

We arrange imaging through an imaging provider when it would change the plan.

Other tests

• Blood tests help find a cause when neuropathy is suspected. Recommended first tests include blood sugar, vitamin B12 with related markers, and protein testing for certain blood disorders. These are usually ordered with your primary care physician or a neurologist.^[10]
• Skin biopsy and other tests can help diagnose small fiber neuropathy, a cause of burning feet. They are arranged with a neurologist.^[11]

Putting it together

We combine your history, the examination, and any test results to reach the most likely explanation. If the results and the examination disagree, we say so and explain what we think is most likely. If you have had tests elsewhere, bring the reports; they can save you a repeat test. Read more about your visit in what to expect, and about a common look-alike in back or foot? finding the source of nerve pain.

When to seek care

Consider an evaluation if burning, tingling or numbness in your foot lasts more than a few weeks, or if you’ve had tests that were normal but your symptoms haven’t gone away.