Sciatica: Causes, Diagnosis, and How Doctors Decide What Comes Next

Written by Ifije Ohiorhenuan, MD, PhD — Board-Certified Spine Surgeon. Last updated 2026-06-20.

Sciatica is pain, tingling, numbness, or weakness that travels from the low back or buttock into the leg because a nerve is irritated, most commonly by a lumbar disc herniation or spinal stenosis.

In my practice, I use the word sciatica as a starting point, not a complete diagnosis. The real question is: which nerve seems irritated, and why?

This article explains what sciatica means, what can cause it, how MRI findings fit in, and how doctors usually decide between time, therapy, injections, and surgery.

What Is Sciatica?

Sciatica is a symptom pattern, not one single diagnosis.

It usually means pain that starts in the low back or buttock and travels down the leg. The pain may go into the thigh, calf, foot, or toes.

Sciatica can feel like:

Sharp pain
Electric pain
Burning pain
Shooting pain
Tingling
Numbness
Leg weakness

Some people feel worse with sitting or bending. Others feel worse with standing or walking. Some notice pain when coughing or sneezing.

Clinically, I think of sciatica as a clue, not a final diagnosis. The next question is: which nerve seems irritated, and why?

A nerve is a cable that carries signals between your spine, brain, and body. A nerve root is the part of the nerve that leaves the spinal canal near the spine. The spinal canal is the main tunnel in the spine where nerves travel.

The word “sciatica” is often used casually for many types of leg pain. But not all leg pain is true sciatica. Doctors try to find the specific nerve and the specific cause.

The Most Common Causes of Sciatica

Sciatica most often comes from irritation of a nerve in the lower back. The lower back is called the lumbar spine.

Lumbar Disc Herniation

A lumbar disc herniation means the soft inner part of a spinal disc pushes out through the outer layer. A spinal disc is the cushion between two spine bones.

A disc herniation can cause sciatica in two main ways:

It can press on a nerve root.
It can cause inflammation, which means swelling and irritation around the nerve.

This often happens at the L4-L5 or L5-S1 levels. These names describe the lower spine bones and the disc spaces between them. L4-L5 means the level between the fourth and fifth lumbar bones. L5-S1 means the level between the fifth lumbar bone and the sacrum, which is the bone at the base of the spine.

Disc-related sciatica often travels below the knee. It may feel worse with sitting, bending, coughing, or sneezing.

The finding matters most when a disc herniation is touching or compressing the nerve that explains the patient’s pain pattern.

Learn more: Lumbar Disc Herniation: A Surgeon’s Patient Guide

Lumbar Spinal Stenosis

Lumbar spinal stenosis means narrowing around the nerves in the lower back.

This narrowing can happen because of:

Arthritis, which means joint wear and inflammation
Thickened ligaments, which are strong bands of tissue that support the spine
Loss of disc height
Bone spurs, which are extra bone growths
Spondylolisthesis, which means one spine bone slips compared with another

Spinal stenosis often causes leg pain, heaviness, numbness, or cramping with standing or walking. Many people feel better when they sit or lean forward, such as over a shopping cart.

This walking-related leg pain is sometimes called neurogenic claudication. That means leg symptoms caused by nerve crowding in the spine during standing or walking.

Learn more: Lumbar Spinal Stenosis: A Plain-Language Guide for Patients

Foraminal Stenosis

The foramen is the side exit tunnel where a nerve leaves the spine. Foraminal stenosis means this tunnel is narrowed.

Foraminal stenosis can irritate one specific exiting nerve. This can cause pain, numbness, or weakness in that nerve’s pattern.

This is a common place where MRI reports can sound scary. But the key is whether the narrowed foramen is on the same side as your symptoms and at a level that fits your pain pattern.

Spondylolisthesis

Spondylolisthesis means one vertebra slips slightly compared with another. A vertebra is one of the bones of the spine.

This slip can narrow the spinal canal or the foramen. That can irritate nerves and cause sciatica-like leg pain.

Degenerative spondylolisthesis is a type related to aging and arthritis. It is common at L4-L5.

Learn more: Spondylolisthesis: When the Bones Slip

Less Common or Non-Spine Causes

Not every buttock or leg pain problem starts in the spine.

Other causes can include:

Piriformis syndrome or deep gluteal syndrome, where a nerve is irritated deep in the buttock
Sacroiliac joint pain, where pain comes from the joint between the spine and pelvis
Hip problems, such as arthritis or tendon irritation
Peripheral neuropathy, which means nerve damage outside the spine
Vascular claudication, which means leg pain from poor blood flow
Other medical causes, including infection, tumor, or inflammatory conditions

Learn more: Sacroiliac Joint Dysfunction: Why It’s Often Missed

Planned future topic: Piriformis syndrome

What Sciatica Feels Like: Symptom Patterns Matter

The path of pain can give clues. It does not give a final answer by itself.

Pain Location Can Suggest Which Nerve Is Involved

Doctors often compare your symptoms with common nerve patterns.

General patterns include:

L4 nerve: pain or numbness toward the front of the thigh or knee area. There may be weakness in the quadriceps, which are the front thigh muscles.
L5 nerve: pain or numbness along the outer leg or top of the foot. There may be trouble lifting the foot or big toe.
S1 nerve: pain or numbness down the back of the calf or outer foot. There may be calf weakness or a reduced ankle reflex. A reflex is an automatic muscle response tested with a small tap.

These maps are helpful, but they are not perfect. Real symptoms often overlap.

Pain patterns are approximate. A doctor matches symptoms with exam findings and imaging before deciding which nerve is involved.

Why Back Pain and Leg Pain Are Different Clues

Sciatica usually means leg symptoms are a major part of the problem.

Back pain alone is not the same as sciatica.

Many people have both back pain and leg pain. The dominant symptom matters. If leg pain is much worse than back pain, doctors often look harder for nerve irritation. If back pain is the main symptom, the treatment path may be different.

Why MRI Findings and Symptoms Must Match

An MRI report may list many findings. MRI stands for magnetic resonance imaging. It is a scan that shows discs, nerves, bones, and soft tissues.

But an MRI finding only matters if it fits the clinical picture.

For example:

A left-sided disc herniation usually does not explain right-sided leg pain.
A severe-looking MRI finding may not be painful if it does not match your symptoms.
A mild-looking MRI finding can matter if it lines up with your pain pattern and exam.

What I look for on MRI is not just whether something looks abnormal, but whether it matches the side and path of the patient’s leg symptoms.

How Doctors Diagnose Sciatica

Doctors diagnose sciatica by putting several pieces together. No single piece is perfect.

History

Your history means the story of your symptoms.

Important details include:

Where the pain starts
Where the pain travels
Whether pain goes below the knee
Where you feel numbness or tingling
Whether you notice weakness
How far you can walk
What positions make symptoms better or worse
How long symptoms have been present
What treatments you have already tried

In many cases, the story gives the first strong clue.

Physical Exam

A physical exam helps check whether a nerve is affected.

This may include:

Strength testing
Reflex testing
Sensation testing, which checks feeling in the skin
Straight leg raise testing
Nerve tension tests
Watching your walking pattern
Hip screening
Sacroiliac joint screening when needed

A straight leg raise test is when the leg is lifted while you are lying down to see if it reproduces nerve-type leg pain.

MRI

MRI shows anatomy. But it does not automatically prove the source of pain.

Doctors look for compression or irritation near a nerve that matches your symptoms. Compression means pressure. Inflammation means swelling or irritation.

MRI reports may use terms such as:

Disc protrusion: a type of disc herniation where the disc pushes out but has a broad connection to the disc
Disc extrusion: a type of disc herniation where the pushed-out disc material has a narrower connection to the disc
Foraminal stenosis: narrowing of the side exit tunnel for a nerve
Lateral recess stenosis: narrowing in the side part of the spinal canal where nerve roots travel
Nerve root impingement: contact or pressure on a nerve root
Canal stenosis: narrowing of the main spinal canal

MRI is most helpful when the findings match the side, level, and pattern of symptoms.

X-rays, CT, and EMG/Nerve Tests

Other tests may help in certain cases.

X-rays are pictures that show bone alignment. They can show arthritis, spondylolisthesis, scoliosis, and signs of instability. Instability means abnormal motion between spine bones.

A CT scan, or computed tomography scan, uses X-rays to show more bone detail. It may help when MRI is limited or when bone anatomy needs a closer look.

EMG/NCS means electromyography and nerve conduction studies. These are nerve tests. They can help when the diagnosis is unclear or when symptoms may come from nerves outside the spine.

Sciatica Treatment: The Usual Stepwise Path

Most sciatica treatment follows a stepwise path unless there are red flags or worsening nerve problems.

In my practice, the decision between time, therapy, injection, and surgery depends heavily on the severity of pain, the presence of weakness, and whether the MRI and symptoms line up.

Activity Modification and Time

Many episodes of sciatica improve over weeks.

That does not mean the pain is “in your head.” Nerve pain can be very real and severe. But inflammation around a nerve can settle with time.

Prolonged bed rest is usually not helpful. Gentle movement is often encouraged, as long as symptoms do not worsen significantly.

Activity changes may include avoiding positions that clearly flare the leg pain. The right approach depends on the cause and your tolerance.

Medications

Medication choices depend on your medical history and risk factors.

Common categories include:

Anti-inflammatory medicines, when medically safe
Acetaminophen
Nerve pain medicines in selected cases
Short courses of other medicines based on clinician judgment

This article does not give dosing instructions. Medication safety depends on kidney function, stomach bleeding risk, blood thinners, liver disease, heart history, and other factors.

Physical Therapy

Physical therapy, or PT, is guided exercise and movement treatment.

PT may focus on:

Mobility
Core strength
Hip strength
Nerve mobility
Posture
Walking tolerance
Graded return to activity

A disc herniation pattern and a spinal stenosis pattern may need different strategies. For example, some disc symptoms flare with bending. Some stenosis symptoms flare with standing and walking.

Good therapy is adjusted to the cause and to what your body can tolerate.

Epidural Steroid Injections

An epidural steroid injection is an injection of anti-inflammatory medicine near irritated spinal nerves. The epidural space is the area around the nerves inside the spine.

These injections are often used for leg-dominant nerve pain. They may be considered when symptoms continue despite nonoperative care or when pain is blocking progress with therapy.

Injections can reduce inflammation around a nerve. They do not fix every structural problem. Relief varies. Some people get strong relief. Some get short-term relief. Some get little benefit.

Planned future topic: ESI vs PT for sciatica

Surgery

Surgery may be considered when:

Severe leg pain does not improve with nonoperative treatment
Leg pain keeps quality of life very limited
Weakness is getting worse
MRI findings clearly match the symptoms
There is a specific problem that surgery can address

Common operations include:

Microdiscectomy: surgery to remove the part of a herniated disc pressing on a nerve
Decompression: surgery to create more room around crowded nerves

The right operation depends on the cause. Disc herniation, stenosis, foraminal stenosis, and spondylolisthesis may require different plans.

Surgery is not always needed. It is also not always avoidable.

When Sciatica Is an Emergency

Most sciatica is not an emergency. But some symptoms need urgent medical care now.

Seek urgent medical care now, or emergency evaluation, if sciatica is associated with:

New loss of bladder or bowel control
Numbness in the groin or saddle area
Rapidly worsening leg weakness
New foot drop
Fever, chills, or concern for infection
History of cancer with new severe spine pain
Major trauma
Severe, unrelenting pain with systemic illness

Foot drop means trouble lifting the front of the foot while walking. Saddle numbness means numbness in the areas that would touch a saddle, including the groin, inner thighs, and buttocks.

These symptoms can be signs of serious nerve compression or other urgent disease.

This article is educational and cannot determine whether your symptoms are urgent. If you have new bladder or bowel problems, saddle numbness, or rapidly worsening weakness, do not wait for an online review.

Learn more: Cauda Equina Syndrome: The Spine Emergency Patients Need to Recognize

How to Read a Sciatica MRI Report Without Panicking

MRI reports are written for medical teams. They often use words that sound alarming.

The words matter. But context matters more.

Words That Sound Scary but Need Context

Here are common MRI terms.

Degenerative disc disease means age-related disc wear. It is common. It does not always cause pain.

Disc bulge means the disc extends beyond its usual border in a broad way. Bulges are common, including in people without symptoms.

Disc protrusion means a more focused disc herniation.

Disc extrusion means disc material has pushed out farther through the outer layer.

Nerve root contact means a disc or bone change touches a nerve root. Contact does not always mean the nerve is the pain source.

Nerve root compression means there is pressure on a nerve root. This matters most when it matches your symptoms and exam.

Foraminal narrowing means the side exit tunnel for the nerve is smaller than usual.

Stenosis means narrowing. It can involve the spinal canal, the lateral recess, or the foramen.

Learn more:

The Three Questions That Matter Most

When I review a sciatica MRI, I focus on three questions:

Is there a finding on the same side as the symptoms?
Is it at a level that matches the pain or numbness pattern?
Is there evidence of nerve compression or inflammation that fits the severity of symptoms?

These questions help separate “an MRI finding” from “the likely pain generator.” A pain generator is the structure most likely causing the pain.

Why “Abnormal” Does Not Always Mean “Dangerous”

Many people have disc bulges, arthritis, or degenerative changes on MRI without pain.

That is why an MRI report should not be read in isolation.

A report may look “bad” but not explain your symptoms. Or a smaller finding may be important if it matches the exact nerve pattern.

The clinical picture matters more than one phrase in the report.

After Treatment: How to Know If the Plan Makes Sense

A good sciatica plan should connect three things:

Your symptoms
Your exam findings
Your imaging findings

For example, if you have right-sided pain down the outside of the leg and top of the foot, the doctor may look for a right-sided finding affecting the L5 nerve. If the MRI only shows a left-sided issue, the plan may need more thought.

When patients are stuck between different recommendations, I try to separate three questions: what the MRI shows, what symptoms it could explain, and what category of next step is reasonable.

That next-step category may be:

More time and activity modification
Physical therapy
Medication adjustment
Epidural steroid injection discussion
Surgical consultation
Urgent in-person evaluation, when red flags are present

Not sure whether your MRI explains your sciatica?
Get a written MRI/case review from a board-certified spine surgeon. SpineClarity helps translate your MRI report into plain language and explains what next-step category may fit your situation — such as continued conservative care, injection discussion, surgical consultation, or urgent in-person evaluation when appropriate.

SpineClarity is not emergency care and does not replace an in-person physician relationship.

Key Takeaways

Sciatica describes nerve-type leg pain, not one single diagnosis.
The most common causes are disc herniation and spinal stenosis.
MRI findings matter most when they match the side, level, and pattern of symptoms.
Many cases improve without surgery, but some require injections or surgery.
Red flags like bladder or bowel changes, saddle numbness, or worsening weakness require urgent care.

Frequently Asked Questions

What is the most common cause of sciatica?

One of the most common causes is a lumbar disc herniation. This is when disc material pushes out and irritates a nerve root in the lower back.

Lumbar spinal stenosis is also common, especially in older adults. Stenosis means narrowing around the nerves.

Can sciatica go away on its own?

Yes, many cases improve over weeks with time and nonoperative care. This is especially common when nerve inflammation settles.

But sciatica does not always go away on its own. Worsening weakness, severe lasting pain, or red flags can change the plan.

How do I know if my sciatica is from a disc herniation?

A disc herniation is more likely when leg pain travels below the knee and is worse with sitting, bending, coughing, or sneezing.

MRI can help confirm whether a disc herniation is touching or compressing the nerve that fits your symptoms. The MRI finding and symptom pattern need to match.

Does sciatica always show up on MRI?

No. MRI may not always show a clear cause. Sometimes symptoms are from inflammation, small nerve irritation, or a non-spine cause.

Also, MRI findings can be hard to interpret without an exam and symptom map.

Can an MRI look bad even if my symptoms are mild?

Yes. Disc bulges, arthritis, and degenerative changes are common, even in people without pain.

A scary phrase on an MRI report does not automatically mean danger or surgery. The key is whether the finding matches your symptoms.

When should I worry about sciatica?

Worry more if you have new bladder or bowel problems, numbness in the groin or saddle area, rapidly worsening leg weakness, or new foot drop.

Fever, cancer history with new severe spine pain, major trauma, or severe pain with systemic illness also needs urgent attention.

Is physical therapy or an epidural steroid injection better for sciatica?

It depends on the cause, pain severity, duration, and whether pain is limiting movement.

Physical therapy may help improve mobility, strength, posture, and activity tolerance. An epidural steroid injection may help reduce inflammation around an irritated nerve, especially when leg pain is dominant.

They are not always competing choices. Sometimes therapy and injection are used at different points in the same treatment path.

When is surgery considered for sciatica?

Surgery may be considered when leg pain remains severe and disabling despite nonoperative care, when imaging clearly matches the symptoms, or when weakness is getting worse.

The type of surgery depends on the cause. A disc herniation may be treated differently than spinal stenosis or spondylolisthesis.

Can piriformis syndrome mimic sciatica?

Yes. Piriformis syndrome, sometimes called deep gluteal syndrome, can cause buttock and leg pain that feels like sciatica.

In that condition, irritation may happen deep in the buttock rather than from a nerve root in the spine. Hip problems, sacroiliac joint pain, neuropathy, and blood flow problems can also mimic sciatica.

What should I do if my MRI report mentions nerve root impingement?

Nerve root impingement means the report describes contact or pressure near a nerve root.

The important questions are whether it is on the same side as your symptoms, whether it matches the pain pattern, and whether it fits your exam findings. The phrase alone does not automatically mean surgery.

References

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Kreiner DS, Shaffer WO, Baisden JL, et al. An evidence-based clinical guideline for the diagnosis and treatment of degenerative lumbar spinal stenosis. Spine Journal. 2013;13(7):734-743. doi:10.1016/j.spinee.2012.11.059

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