Sciatica Cause Not Always Spine-Related

Some medical conditions can mimic sciatica

The term “sciatica pain” is commonly used to describe pain that radiates from the low back into a leg. The most common cause of sciatic nerve pain is usually a herniated disc. However, there are many causes of sciatica symptoms beyond the spine; sometimes called non-spinal pathology—a diagnosis not related to the spine. Some non-spinal causes of sciatica can mimic the symptoms of a painful herniated disc in the lower back.
Man in exercise clothing, holding his low back Several disorders not spine-related can cause sciatica pain and symptoms. Photo Credit: Jan-Otto. Photo Source: iStock.com.When a lumbar herniated disc causes sciatica, people typically report a sudden onset of pain with leg pain worse than any back pain that might be present. In addition to pain in their leg, some people report leg weakness and altered sensation, such as numbness or tingling. The leg pain is usually made worse by long periods of sitting or standing, forward bending, and maneuvers that increase pressure within the intervertebral discs—also known as Valsalva Maneuvers—such as coughing or sneezing. Lying down and extending the back tends to alleviate the pain.

When trying to determine the source of sciatica pain symptoms, it is important to be able to characterize the events leading up to the onset of symptoms, the location of the pain and associated symptoms, factors that alleviate and exacerbate the pain, and any medical history that may be relevant, such as a history of cancer. Given the many non-spinal causes of sciatica, it can be helpful to keep in mind the following:

  1. The course of the sciatic nerve. It starts as a coalition of the lower lumbar and upper sacral nerve roots, exits through the pelvis, runs down the back of the thigh to the knee, where it branches into the two major nerves that provide motor and sensory function to the leg and foot.
  1. The broad categories of non-spinal sciatica. Non-spinal causes of sciatica symptoms usually result from irritation of the sciatic nerve itself. The most common ways to “irritate” a nerve is compression, traction, or intrinsic injury to the nerve itself.
  1. Symptoms we perceive as sciatica may not be related to the sciatic nerve at all. Injury to structures close to the sciatic nerve, like the hip joint, can mimic the symptoms caused by irritation of the sciatic nerve.

Hip joint disorders can mimic sciatica symptoms

Given the close proximity of the sciatic nerve to the hip joint, it is not surprising that injury to the hip joint can mimic symptoms of sciatica. Regardless of the cause of a hip injury, most people with hip pathology report pain in the groin, upper thigh, and buttocks. The pain is made worse with activity, particularly flexion and internal rotation of the hip.

Leg pain that results in a limp when walking makes it more likely that the hip, rather than the lower back, is the source of the leg pain. Radiographs (x-rays), and in some cases MRI, of the hip can be helpful to determine whether the hip is the cause of leg pain. Examples of hip pathology that can mimic spine related sciatica include:

  • Hip Osteoarthritis: Characterized by loss of cartilage of the femoral head and acetabulum resulting in narrowing of the “ball and socket joint.” In people with arthritis of the spine and hip, a hip joint steroid injection can be both therapeutic (provides pain relief) and diagnostic (helps to identify the primary pain generator).

labeled anatomical picture illustration of the hip jointsAnatomical illustration of the body’s hip joints, sacrum, sacroiliac joints and adjacent structures. Photo Credit: medicalstocks. Photo Source: iStock.com.

  • Osteonecrosis: Collapse of the femoral head due to lack of blood flow. Risk factors for osteonecrosis include a history of alcohol abuse, sickle cell disease, chronic steroid use, femoral neck fracture, and hip dislocation.
  • Femoroacetabular Impingement (FAI): Repeated abnormal contact between the femoral neck and acetabulum due to a bony deformity of the femur (thighbone) and/or acetabulum. Impingement at the hip joint can cause early arthritis and tears of the labrum (a type of cartilage that surrounds the hip joint and helps provide stability to the hip joint).
  • Greater Trochanteric Bursitis: Bursas are fluid filled sacs that help decrease friction between bone and surrounding tendons and muscles. They are present at multiple locations around the body. Bursitis refers to inflammation of a bursa and can be quite painful. The greater trochanter is a bony protuberance or outward bony bump extending laterally from the proximal femur. Putting it all together, greater trochanteric bursitis, refers to painful inflammation of the bursa that separates the lateral margin of the bony greater trochanter with the muscles and tendons of the lateral thigh. It is characterized by pain on the outside of the thigh that is made worse by pressing over the painful area and can disrupt sleep when lying on the affected side.
  • Femoral Neck Stress Fracture: An incomplete fracture of the femoral neck that typically occurs in people who walk or run long distances on a regular basis, such as runners and soldiers. The pain localizes to the groin and can be subtle in onset. Walking or running will make the pain worse.

Sacroiliac joints, sacral fractures may replicate sciatica

The sacroiliac (SI) joints connect the spine to the pelvis. There are two SI joints, one on either side of sacrum. While these two joints are relatively immobile, they are subjected to tremendous force during routine, daily activities. Examples of SI joint pathology that can mimic spine-related sciatica include:

  • Sacroiliitis: Inflammation of the SI joints. The pain begins slowly with no obvious inciting event. It localizes to the buttocks and can cause radiating pain down the back of the thigh. This is thought to be due to either irritation of the sciatic nerve by the inflammatory molecules present in the SI joint or referred pain from the SI joint—pain that is perceived to be in a location other than the location of the pain generator. Pain due to sacroiliitis tends to improve with light walking.

Anatomical picture illustration depicting inflammation of the sacroiliac jointAnatomical illustration of sacroiliitis. Photo Credit: medicalstocks. Photo Source: iStock.com.

  • Sacral Insufficiency Fracture (SIFs): A fracture of the sacrum that occurs in people with weakened bone after a minor injury or without trauma. Risk factors include advanced age, osteoporosis, chronic steroid use, rheumatoid arthritis, and vitamin D deficiency. Pain usually localizes to the low back and radiates to the buttocks and/or groin and is made worse with activity.

Trauma induced sciatica

There are numerous ways in which trauma to the pelvis or thigh can cause sciatica pain and symptoms. In cases of high-energy trauma, it is possible for the nerve roots that form the sciatic nerve to become pulled or torn (called avulsed). While relatively rare, nerve root avulsions have been documented in the literature, with MRI usually aiding in the diagnosis.

More common traumatic causes of sciatica include traction-induced sciatica from a posterior hip dislocation or a pelvic fracture. The hamstring muscles (biceps femoris, semitendinosus, and semimembranosus) lie in close proximity to the sciatic nerve. A hamstring tear can irritate the sciatic nerve either through direct compression from the resulting localized bleeding (called a hematoma) or by the inflammatory response triggered at the time of injury.

anatomical illustration of the hamstring muscles in the thighAnatomical illustration of the hamstring muscles: biceps femoris, semitendinosus, and semimembranosus that lie in close proximity to the sciatic nerve. Photo Source: iStock.com.

Penetrating trauma—when an object such as a knife or bullet violates the skin—can cause sciatica by cutting across the nerve (called direct transection) or tearing the  nerve (called laceration). In cases of ballistic trauma (ie, gunshot wound), direct transection of the nerve is quite rare. Most cases of bullet-induced sciatica result from a mild type of nerve injury (called neuropraxia) that temporarily blocks nerve function. Neuropraxia may develop from shock waves that surround the bullet as it travels through tissue.

Benign tumors and metastatic cancer are rare sciatica causes

Uncovering a new cancer during a workup of sciatica is exceedingly rare. Symptoms that may raise the likelihood of cancer being the cause of sciatica include the “red flag” symptoms that are often discussed in the context of new onset back pain:

  • History of cancer
  • Age greater than 50 years
  • Leg pain that persists at night and is not relieved by lying on your back
  • Night sweats
  • Unexplained weight loss

Back pain that begins in a subtle manner without history of trauma and is not affected by activity or changes in position may also suggest an oncologic origin.

How does a tumor cause sciatic pain and symptoms?
Tumors usually cause sciatica by direct compression on the sciatic nerve and can be benign or malignant. The tumor can arise from the sciatic nerve itself (types of nerve tumors include neurofibroma and schwannoma), surrounding tissue (eg. fatty tissue called lipoma), or as metastases from a distant source (eg. lung cancer).

Shingles may mimic sciatica

Shingles, also known as herpes zoster, is a painful rash that occurs on only one side of the body. It is caused by the varicella zoster virus; the virus that causes “chickenpox.” Once someone has been exposed to the virus, usually during childhood, the virus can lie dormant in nerve cells for years without causing any symptoms. Older age or conditions that put someone in an immunocompromised state can cause reactivation of the virus. When the virus is reactivated in the location of the buttocks and thigh, it can mimic the symptoms of sciatica. The presence of a red rash with blisters in the region of pain is consistent with shingles.

Childbearing and endometriosis

During pregnancy, the lumbosacral plexus in the pelvis can be compressed between the growing fetus and the bones in the pelvis. Prolonged lithotomy positioning (having hips and knees flexed and supported by stirrups) can also cause sciatica. Fortunately, pregnancy associated sciatica is most likely to be temporary.

A less common cause of sciatica that tends to occur in women of reproductive age is endometriosis. Briefly, endometriosis is the growth of endometrial tissue in a location other than the uterus, usually the ovaries and fallopian tubes. In some cases, endometrial tissue can accumulate in areas that surround the sciatic nerve or the sciatic nerve itself. As the endometrial tissue responds to the changes in hormones that take place during a normal menstrual, cyclical and recurrent sciatica pain can occur.

Vascular diagnoses

Abnormal arteries and veins in the pelvis and lower extremities can cause sciatica symptoms by either compression or ischemia (lack of oxygen due to inadequate blood flow). An aneurysm can occur when the wall of the artery weakens to the point where it cannot withstand the pressure of the blood flowing through it. This leads to enlargement of the artery. In some cases, the artery grows large enough to compress the sciatic nerve.

Peripheral artery disease can lead to sciatica when it progresses to the point where not enough blood is circulated from the heart to the muscles in the legs. When there is not enough oxygen being delivered to the muscles, leg pain and numbness can occur. This is sometimes called vascular claudication and is characterized by pain that is aggravated by walking and relieved by standing still. Risk factors for peripheral artery disease include people who smoke or have smoked in the past, people with high blood pressure, high cholesterol, or are diabetic.

Diabetes and high blood sugar

Diabetic peripheral neuropathy occurs due to nerve damage from elevated blood sugar. Nerves that have been exposed to chronically elevated blood sugar can become damaged due to disruption of blood flow in the small blood vessels that supply the nerve, or by altering the cellular structure of the nerve itself.

Prescription medications

Nerve and muscle damage can also occur as a side effect from a wide range of medications. Malfunctioning nerves (neuropathy) and muscles (myopathy) can cause symptoms that mimic those of sciatica caused by disc herniation. In some cases, the symptoms abate when the offending medication is discontinued. While the list of medications that can cause neuropathy and myopathy are is too extensive to list here, common culprits include various chemotherapy agents, antibiotics, and statins (a class of medication that helps lower cholesterol).

Piriformis Syndrome, Wallet Sciatica

Piriformis syndrome and wallet sciatica are the final two topics to discuss in our overview of extraspinal (non-spinal) causes of sciatica.

The piriformis is a muscle that originates on the sacrum, runs through the sciatic notch, and attaches to the to the top of the femur. Also running through the sciatic notch is the sciatic nerve. Piriformis syndrome is caused by the piriformis muscle compressing the sciatic nerve. People with this syndrome typically report pain in the buttocks and shooting pain down the same leg that is made worse by sitting. Piriformis syndrome can be difficult to diagnose and tends to be a diagnosis of exclusion, meaning examination and test results may not be conclusive for a piriformis diagnosis. Various physical exam maneuvers have been developed to aid in the diagnosis of piriformis syndrome. They usually involve some form of resisted hip abduction and/or external rotation as these maneuvers cause contraction of the piriformis muscle.

anatomical illustration of the piriformis muscle and sciatic nerveAnatomical illustration of the piriformis muscle and sciatic nerve. Photo Source: Shutterstock.

Credit-card-wallet sciatica, wallet neuritis, and wallet sciatica are all terms that have been used to refer to compression of the sciatic nerve by a large wallet located in the someone’s back pocket. While this may sound like a made-up phenomenon, reports of sciatica caused by a bulky wallet have been reported in some of the most prestigious medical journals since the 1960s. Similar to symptoms of piriformis syndrome, wallet sciatica presents as buttocks and single leg pain that is aggravated by sitting. Treatment in the form of a walletectomy (removing the wallet from the back pocket) tends to provide substantial pain relief.

Summing Up Non-spinal Sciatica Causes

In conclusion, while the majority of sciatica cases are caused by a lower back spinal disorder (eg, lumbar herniated disc), there are numerous causes of sciatica due to extraspinal pathology—that is, causes outside the spinal column. Being able to precisely describe the location and quality of the pain, associated symptoms, and factors that aggravate and alleviate the sciatic-type pain can help you and your doctor arrive at an accurate diagnosis and appropriate treatment plan.

Updated on: 02/05/20
Continue Reading
What You Need to Know About Sciatica Now
×
SHOW MAIN MENU
SHOW SUB MENU
Cancel
Delete
Continue Reading:

What You Need to Know About Sciatica Now

Spine surgeon discusses sciatica symptoms, causes, diagnosis and non-surgical treatments that manage back pain and leg pain.
Read More