Introduction

Pain is an unpleasant sensory and emotional perception that is usually, but not always, the result of underlying tissue pathology. It is often the initial complaint that brings a patient to the physician’s office and is the primary chief complaint in the emergency department. Clues to diagnosis will always begin with the history and exam of the patient but the history can sometimes be difficult to obtain, as pain can be difficult to describe for each patient. Accepted descriptions of pain in the medical literature can include “tingling,” “numbness,” “zinging,” “dull,” “sharp”, “stabbing”, “throbbing,” and “aching.” All of these descriptors carry different meaning to different patients, depending upon culture, language, or prior experiences. The temporal nature of pain further complicates the pain experience, whether pain is acute or chronic, or acute on chronic. Together these factors will change the description of pain in the patient’s history.

Pain is a complex problem that is affected by physical and psychological factors. Further complicating the history taking, aside from the ability to describe pain, is the interpretation by the provider. Again, this is determined by culture, language, and prior pain experiences, but on the part of the provider. With no gold standard diagnostic test for pain, the interpretation really does depend upon this interaction between provider and patient. These challenges all contribute to the proper or improper diagnosis and treatment of the patient.

Patients in the current multidisciplinary healthcare model are often referred to specialists without a clear etiology for their pain. Referrals from specialists who are resigned to not knowing the cause of a patient’s pain from diagnostic tests make it that much more difficult to ascertain the cause of pain with unknown etiology, and patients’ expectations can sometimes add to the care burden. Pain can be seen as a neurologic problem, though neurologists are not specifically trained to treat pain. Neurology training is focused on acute stroke and eventually stroke prevention as well as chronic disease such as Parkinson disease, Alzheimer disease, and movement disorders. However, the nervous system becomes the conduit for recognizing pathology in the body; hence, unknown etiologies become a neurologic issue in the absence of a neurologic etiology.

The history of pain is complex, as it is related to the previously mentioned factors, which include experience, culture, language, anatomy, and actual neurologic lesions. However, pain has been a part of human history since ancient times; some civilizations have believed that pain was caused by evil spirits or demons and that it could be removed by rituals. With the inception of religious belief, pain was similarly attributed to punishment and sin. Hippocrates (460–377 BCE) argued that disease came not from a superstition or a god but rather was a natural process. Galen (CE129–216) believed that pain was an interconnected phenomenon between the mind/soul and the body. Descartes, during the 17th century, brought about the mechanistic model of pain by separating the body and the soul and medicalizing the pain condition. Not long afterward, Thomas Willis laid the foundation for neurology in the 17th century through his study and description of brain anatomy and the nervous system and explaining how sensory information, such as pain, is transmitted. Johannes Muller in the 1830s theorized that the perception of sensory stimuli was due not to the original stimuli, but to the activation of specific nervous structures and partially explained why different types of pain are perceived differently by the specific nervous system activation pattern. In the 1960s Wall and Melzack proposed the gate control theory, whereby the experience of painful stimuli is affected by the nonpainful stimuli through inhibition of the nervous system signal. The gate control theory has helped lead to treatment of pain through the use of technological devices such as spinal cord stimulators by which pain transmission is altered in the dorsal columns of the spinal cord.

Acute pain is typically short term and the result of an injury or a specific event. Chronic pain lasts for an extended period, usually more than 3 months and can be the result of an underlying medical condition, injury, or disease. Pain may be localized or radiating, spreading from its source to other areas of the body. Nociceptive pain is caused by activation of nociceptors, which are pain receptors in body tissue, and may be somatic, arising from skin, muscle, or joints, or may be visceral, related to internal organs. Neuropathic pain results from dysfunction or damage of the nervous system. Pain intensity can range from mild to severe, and various pain scales, such as the Numeric Rating Scale or the Visual Analog Scale, are used to assess and categorize pain based on severity. Referred pain is appreciated in an area that is removed from the source of the problem. An example is left arm pain occurring as a result of a heart attack.

When the primary complaint is pain, the history is often nonspecific, presenting a challenge to the clinician who is trying to determine whether the cause is benign or due to a serious illness. Obtaining a pain history includes location, duration (acute or chronic), exacerbating and relieving factors, and accompanying symptoms. Understanding the neurologic basis of pain is important in establishing a diagnosis and treatment plan. Knowing the different types of pain is important, as each pain requires a different treatment approach. This chapter aims to help rule out neurologic causes of pain and includes several of the most common presentations of pain that often prompt a neurology referral for further workup, focusing on common neurologic causes of pain seen in the primary care physician’s office ( Box 27.1 ). Diagnostic testing and an initial treatment for these disease pathologies will also be reviewed briefly.

Low Back Pain

Low back pain is listed as one of the top 10 diseases in the population, and the prevalence is increasing with longer lifespans. It is one of the most common complaints in the primary care physician’s office. Healthcare costs for low back pain are not insignificant, with low back and neck pain having estimated healthcare costs of over $87 billion in 2013, just behind ischemic heart disease. Referrals to neurologists and pain physicians are often made for chronic axial low back pain and lumbar radiculopathy. Common causes of low back pain are listed in Box 27.2 .

The physical examination is extremely important in the evaluation of low back pain. Red flag symptoms include focal neurologic deficits such as motor weakness, bowel and/or bladder changes, saddle anesthesia, or asymmetry in reflexes and/or strength indicating a cauda equina syndrome where there is a dysfunction of multiple lumbar and sacral nerve roots at the end of the spinal cord referred to as the cauda equina due its resemblance to the tail of a horse. All of these symptoms mandate an expedited evaluation with magnetic resonance imaging (MRI) of the spine ( Box 27.3 ). Initial workup may reveal disc herniation, causing severe spinal stenosis or more serious concerns, such as infection, compression fracture, and malignancy. Presentation of red flag symptoms can be acute or subacute in nature meaning from days to weeks, and patients may require surgical intervention in the first 48 hours. With regard to the characterization of pain, however, pain is defined as acute if it has been present for less than 3 months. Chronic low back pain, by contrast, is defined as pain lasting more than 3 months. Chronic pain affects 619 million people worldwide, according to the World Health Organization, with an estimated number of 843 million by 2050. These numbers are expected to increase due to the increasing global aging population and it is the leading cause of disability worldwide.

Nonspecific low back pain can be attributed to several causes, including the following:

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  Degenerative disc disease: The intervertebral discs in the spine are under constant pressure. With age, they begin to decrease in thickness. These discs begin to lose their cushioning ability in the spine over time and can cause significant pain and stiffness in the low back and may lead to a decrease in motion.

  
  
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  Herniated disc: The intervertebral discs begin to bulge with age and can put pressure on the spinal cord and spinal nerves. The disc is composed of an outer ring called the annulus fibrosus, which surrounds a gel-like center called the nucleus pulposus. A rupture in the disc is called a herniation, and the nucleus pulposus can leak, causing irritation of the spinal nerve roots with resulting low back and/or sciatic pain.

  
  
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  Spondylolisthesis: This is a condition in which a vertebra slips out of alignment of the spine, putting pressure on the spinal cord and/or nerve roots. Spondylolisthesis can also cause low back and/or sciatic pain, depending on the location of the compression.

  
  
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  Arthritis: The facet joints in the spine provide flexibility and stability. With age and degenerative changes, the facet joints of the spine can become arthritic, causing pain anywhere along the spine, and can be a major contributor to low back pain with age. Interestingly, rib cage support is one reason that low back and neck pain are more prevalent than mid-back pain.

  
  
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  Spinal stenosis: Narrowing of the spinal canal due to aging and arthritis. The narrowing can cause impingement of the nerve roots as well as compression of the spinal cord itself and again can cause low back or sciatic pain depending on the location. The pain, often referred to as neurogenic claudication, is intermittent and worsens with activities such as standing or walking. Sitting and bending at the waist tend to relieve the pain.

  
  
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  Muscle strain: Any injury or strain of the back musculature can cause pain, stiffness, and decreased range of motion in the lower back.

  
  
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  Osteoporosis: Decreased bone density with age increases the risk of spine compression fractures. Osteoporosis itself is not usually symptomatic until fractures occur, which can be extremely painful and debilitating.

  
  
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  Psychological factors: Stress, anxiety, and depression all can exacerbate underlying pain diagnoses.

Treatment for chronic low back pain depends on the underlying etiology. For the primary care provider, the key decision is in referring for surgical treatment versus conservative therapy. In most cases, conservative therapy should be tried before proceeding to surgical intervention. These treatments include the following:

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  Physical therapy (PT): Strengthening of the lumbar musculature helps to stabilize the spine and can increase the range of motion. PT can also help with conditions such as spinal stenosis, in which bending forward can relieve the pressure on the spinal cord.

  
  
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  Ice and heat therapy: Ice therapy can be utilized for treatment of low back pain by decreasing inflammation of the lumbar musculature with ice. Heat can help with muscle loosening and relaxation.

  
  
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  Transcutaneous electrical nerve stimulation (TENS): There is conflicting evidence as to the efficacy of TENS. TENS therapy consists of a low-voltage electric current applied by electrodes attached to the skin on the low back overlying the area of pain. The electric impulses can theoretically decrease pain by modifying the transmission of pain signals. Another theory is that TENS can increase the level of endorphin production in the body, thereby decreasing the pain levels. The therapy is sometimes used in conjunction with PT.

  
  
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  Yoga: There is increasing evidence for yoga as a tool for decreasing low back pain. Like PT, yoga strengthens and stretches back muscles and can improve range of motion through stabilization of the spine.

  
  
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  Massage therapy: Often combined with PT, massage therapy helps with improving tissue elasticity, reducing scar formation, decreasing inflammation, and increasing blood flow to tissues.

  
  
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  Chiropractic treatment: While chiropractic treatment is controversial, some evidence does show that it can help with decreasing low back pain in several measures, such as pain intensity, disability, and decreased use of pain medicine.

  
  
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  Acupuncture: Another less-accepted method of treatment, acupuncture has also shown some evidence for low back pain treatment. Acupuncture is thought to trigger release of endorphins as well as release of neurotransmitters in the brain, altering some of the pain pathways.

  
  
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  Percutaneous injections: Percutaneous injection is a more accepted treatment of targeted steroid injections for reducing pain and inflammation at the joints or at the nerve roots, decreasing pain transmission at the source of the pain.

  
  
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  Medication: Over-the-counter pain medications such as ibuprofen, naproxen, and acetaminophen are very effective at reducing inflammatory mediators. Muscle relaxants are another class of medications that can be used, especially in the case of myofascial pain. Some evidence has shown certain antidepressants such as the serotonin and norepinephrine reuptake inhibitors (SNRIs) to be effective at helping to control chronic pain.

Radiculopathy

Establishing the etiology of low back pain can be challenging, as there can be an extremely varied presentation. A patient can present with descriptions of pain that include dull aching pain, shooting pain, tingling, weakness, numbness, and sharp and stabbing pain. “Sciatica” is a common complaint for nerve pain, or radiculopathy, usually characterized as a shooting pain going down one or both legs because of the association with the sciatic nerve. Radiculopathy is not confined to the lower extremities and may emanate from the cervical spine, radiating down the arms or from thoracic pathology around the chest. These radiculopathies are named anatomically for the origin of the nerve impingement in the spine, with cervical radiculopathy for pathology coming from the neck, and thoracic and lumbar radiculopathies named by their respective spinal regions ( Fig. 27.1 ).

Dermatomes of spinal sensory nerve roots (Boileau Grant JC. Grant’s Atlas of Anatomy , 5th ed.; 1962.)

The cause of nerve root impingement can result from anything that decreases the diameter of the neural foramen, causing nerve root compression. In most cases, this is caused by disc herniation, especially in older adults over age 65 years. Other causes can include osteophyte formation (bone spurs), facet hypertrophy, and ligamentous hypertrophy. All of these can cause impingement of the nerve root at the level of its exit from the spinal canal.

Treatment of radiculopathy in the absence of red flags includes initial conservative therapy with neuropathic medications such as gabapentin, and topiramate. Pregabalin has been shown in small studies to be effective in the treatment of radiculopathy, though a recent study found it to be ineffective in the treatment of sciatica. Referral for epidural steroid injections can be done for short-term relief. In intractable cases, surgery can be offered in the setting of imaging findings or in more serious cases with focal neurologic deficits. For intractable cases without clear imaging findings, newer technologies and medications have been explored. One of these technologies is spinal cord stimulation, which is a device consisting of a stimulating wire connected to a generator and implanted over the spinal cord preventing the pain signal from being sent from the spinal cord to the brain.

Neck Pain

Neck pain is a common, often debilitating condition and is the fourth leading cause of disability. Most acute episodes resolve spontaneously, but more than one-third of individuals will experience chronic discomfort that can interfere with their normal daily activities. The history and exam will help to determine whether the pain is mechanical-nociceptive or neuropathic and will also help to identify more serious pathology such as myelopathy or atlantoaxial subluxation. There are numerous causes of neck pain, including the following:

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  Musculoskeletal pain due to trauma from a fall or whiplash injury resulting in strain, sprain, or injury to muscles, ligaments, or joints in the neck.

  
  
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  Inflammatory disorders such as rheumatoid arthritis.

  
  
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  Nerve root compression resulting in radiculopathy due to a herniated nucleus pulposus or bone spur.

  
  
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  Degenerative changes such as cervical spondylosis.

  
  
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  Psychological factors that may contribute to the development of neck pain or exacerbate existing discomfort.

Chronic neck pain occurs when the brain becomes more sensitive to pain signals due to central sensitization amplifying the perception of pain. Changes in function and structure can then perpetuate the pain.

MRI of the cervical spine should be performed when there are focal neurologic symptoms or findings on exam or if the pain is refractory to standard treatment. A scan should also be obtained prior to interventional treatment. However, it should be noted that the imaging is characterized by a high prevalence of abnormal findings in asymptomatic individuals.

Effective management of neck pain requires a multidisciplinary approach. NSAIDs and muscle relaxants are effective for acute pain. There is strong evidence to support exercise treatment, with weaker evidence supporting acupuncture, massage, spinal manipulation, and yoga. There is weak evidence that supports epidural steroid injections and radiofrequency ablation for facet arthropathy and cervical radiculopathy. Surgery is more effective in the short term but not the long term in patients with radiculopathy or myelopathy. Younger patients with greater disease burden and small spinal canal tend to fare better with surgery than older patients with greater function and transverse spinal canal diameter. Cognitive behavioral therapy and relaxation for chronic neck pain can address psychological factors contributing to the pain and lifestyle modification can be beneficial.

Common Neuralgias in the Primary Care Setting and Peripheral Nerve Compression

Entrapment neuropathies caused by compression is the most common cause of mononeuropathies. It is another common disorder in presentation in the primary care office setting, carpal tunnel syndrome being the most common. Other common entrapment neuropathies that are seen in the primary care setting include ulnar neuropathy and meralgia paresthetica. Cervical radiculopathy should also be considered here. For example, pain traveling down the upper extremity into the last two digits can present as either a C8 cervical radiculopathy or an ulnar neuropathy. C6 or C7 radiculopathy can present similarly to carpal tunnel syndrome. As was previously noted, along with a history and physical exam, EMG and/or cervical spine imaging can be helpful in determining peripheral causes of pain.

Trigeminal Neuralgia

There are several causes of intermittent facial pain. Commonly seen in the primary setting include trigeminal neuralgia and occipital neuralgia. Trigeminal neuralgia pain is usually described as short-lasting intermittent jabs or shocks in one of the three divisions of the trigeminal nerve, most commonly the mandibular and maxillary branches. It can be triggered by light touch, toothbrushing, eating, or even talking. The pain is often debilitating, and sometimes patients will present with a half-shaved face or partially applied makeup because of the inability to touch the affected side of the face without pain.

The trigeminal nerve is composed of three anatomic segments: the ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions. More urgent diagnoses should be ruled out in evaluating a patient for facial pain and suspected trigeminal neuralgia. Other headache subtypes and, importantly, temporal arteritis can present similarly in the ophthalmic (V1) division of the trigeminal nerve ( Fig. 27.2 ).

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