Chronic low back pain: Clinical sciences

Chronic low back pain is a common patient concern that can have many underlying causes, including conditions that affect the nerves, joints, bones, muscles, and other soft tissues. Common causes of chronic low back pain include neuropathic pain due to nerve damage, and nociceptive pain due to myalgia, arthralgia, ostalgia, and referred visceral pain.

When a patient presents with chronic low back pain, first, obtain a focused history and physical exam. History typically reveals low back pain that has lasted three months or more, while physical exam might reveal limited range of motion of the spine, tenderness to palpation over the spine or paraspinal tissue, and in some cases, overlying edema or erythema. With these findings, you can diagnose chronic low back pain. To find the cause of low back pain, you should first assess for neuropathic pain. This type of pain is described as lancinating, electrical, radiating, burning, or cold in nature.

Lets first look at If neuropathic pain is present. In this case the patient might report a history of numbness and tingling, as well as radicular pain, which is pain radiating down one or both legs. Physical exam may reveal allodynia, which is when pain is elicited from a stimulus that doesn’t usually cause pain, like a feather. They may also have a positive straight leg raise test, decreased patellar or Achilles reflexes, dermatomal sensory deficits, and myotomal strength deficits. With these findings, diagnose neuropathic chronic low back pain.

Here’s a clinical pearl! There are many possible causes of neuropathic chronic low back pain. For example, a herniated vertebral disc causing spinal nerve root impingement can lead to radicular pain.

Alternatively, lumbar spinal stenosis, which occurs due to degenerative narrowing of the spinal canal, can cause nerve root impingement and subsequent back pain, numbness, and weakness of the lower extremities. Finally, postherpetic neuralgia can cause neuropathic chronic low back pain. This type of back pain occurs initially when a patient develops a herpes zoster rash on their back, and may continue long-term in the distribution of the rash.

Alright, when it comes to treatment, start with lifestyle modifications including continued activity as tolerated. If needed, recommend physical therapy. Pharmacologic therapy includes nonsteroidal anti-inflammatory drugs, or NSAIDs, acetaminophen, muscle relaxants, or serotonin and norepinephrine inhibitors, also known as SNRIs. Anticonvulsants, like gabapentin, might be helpful to some patients with neuropathic pain as well. You can also consider prescribing opiates, but only if other medications fail to control the pain.

Moreover, if your patient’s symptoms are not improving, you can obtain a surgical consult for minimally invasive interventions such as epidural spinal injections or spinal cord stimulation. Surgery can also be an option if patients with severe symptoms fail to have them resolve with less invasive therapy.

Alright, if neuropathic chronic low back pain is not present, assess for nociceptive pain. This type of back pain is localized and usually described as dull or sharp. It does not radiate, has an identifiable pain source, and usually involves joints, bones, muscles, or soft tissues. If this is the case, diagnose nociceptive chronic low back pain.

Next assess the primary tissue involved to determine the source of the pain. Starting with arthralgia, history typically reveals back stiffness and possibly fatigue, malaise, and pain in multiple joints. The exam may show a limited range of motion of the spine or spinal deformity. If this is the case, suspect arthralgia.

Labs like blood work are not typically indicated with suspected arthralgia. However, if you think there’s an underlying inflammatory disease, you can order human leukocyte antigen B27, or HLA-B27, as well as inflammatory markers such as ESR and CRP. Additionally, you can order an x-ray. Labs might be normal, or your patient may have a positive HLA-B27, an elevated ESR and CRP, possibly indicating ankylosing spondylitis. The x-ray might demonstrate sacroiliitis characterized by small erosions and subchondral sclerosis. In either case, diagnose arthralgia.

Time for a clinical pearl! Common causes of arthralgic low back pain include osteoarthritis, ankylosing spondylitis, and psoriatic spondylitis.

Osteoarthritis is the most common cause of back pain in primary care. This degenerative disease of the joints is characterized by mechanical wear and tear injury to articular cartilage, resulting in bony and synovial damage.

Ankylosing spondylitis is a chronic inflammatory illness, more common in biological males, that can result in disabling spinal arthritis. Some patients with this disease carry the HLA-B27 gene. Finally, psoriatic spondylitis is another inflammatory condition. These patients often have additional symptoms such as psoriasis, uveitis, peripheral edema, dactylitis, and pitting of the fingernails.

Okay, let’s talk about treatment for lower back arthralgia. Lifestyle modifications include aerobic and strengthening exercises, as well as hydrotherapy. Some patients may benefit from physical therapy.

Pharmacologic therapy includes NSAIDs with or without acetaminophen. In patients with ankylosing spondylitis, you can consider disease-modifying antirheumatic drugs, or DMARDs, like sulfasalazine. You can prescribe corticosteroids, like prednisone, but only for short-term treatment. Again, opiates are an option only if other medications fail to control the pain.

Lastly, you might need to obtain a surgical consult for minimally invasive spinal interventions, such as facet joint or sacroiliac joint injections, or surgery for those with persisting symptoms despite less invasive therapy.

Next up is ostalgia, also known as bone pain. These patients are usually over 50 years old and may report chronic steroid use or unintentional weight loss. The physical exam reveals spinal tenderness to palpation, and there might be an obvious spinal deformity. In this case, suspect ostalgia.