Karl E. Misulis, MD, PhD
CHAPTER CONTENTS
◦Localization and Diagnosis of Pain Syndromes
◦Management of Neuropathic Pain
OVERVIEW
Pain can be classified into different types that have anatomic, physiologic, and symptomatic distinctions:
FEATURES: Shooting, stabbing, or burning; abnormal perception of temperature
Cause: Neuropathy from any cause, tumor infiltration, ischemia
FEATURES: Deep steady pain especially abdominal or pelvic, often with intermittent paroxysms
Cause: Distortion or distension, ischemia, infiltration
FEATURES: Deep muscular-area pain that may be crampy and movement-related
Cause: Trauma, inflammation, ischemia
FEATURES: Bone-area pain, often deep and with activity-dependent exacerbations
Cause: Trauma, arthritis, ischemia, tumor
FEATURES: Aching pain with tenderness
Cause: Ischemia from occlusive disease, inflammation
Neuropathic pain has a character that depends on the involved nerves but also on the nerve types:
•Large-fiber neuropathic pain is typically shooting or stabbing. Large-fiber pain may be associated with cutaneous sensory loss, but may be less noticeable than the sensory deficit of small-fiber neuropathy.
•Small-fiber pain is more steady, dull, aching or burning. Small-fiber neuropathic pain is often accompanied by impaired sensation of pain and temperature.
Neuropathic pain syndromes encountered in hospital practice can include:
•Peripheral neuropathy: Diabetic peripheral neuropathy is the most common cause and is usually characterized by distal burning pain and sensory loss.
•Mononeuropathy: Compression or infarction of single nerves can cause both small- and large-fiber pain in the distribution of the nerve.
•Plexopathy: Compression, section, infiltration, or inflammation of either the lumbosacral or brachial plexus can cause prominent pain and often weakness.
•Cranial nerve pain: Trigeminal neuralgia is the most common cranial nerve pain. Glossopharyngeal neuralgia is occasionally seen.
Muscular pain can be generated in the muscle fibers, associated nerves, or surrounding tissues. Some of the most common syndromes of muscle pain are:
•Muscle cramp: Often this is precipitated by a specific movement. There is often palpable muscle contraction with the cramp. Causes are many, from local muscle and innervating nerve damage to inflammation. Generalized or multifocal cramps often have a metabolic cause.
•Muscle pain with exertion: Muscle pain and cramp is common after exertion, even in athletes. This can be exacerbated by coexistent fluid or electrolyte disturbance.
Pain may bridge some of the subdivisions; for example, limb injury may result in a combination of muscular, skeletal, and neuropathic pain.
Localization and Diagnosis of Pain Syndromes
Localization and characterization of the pain are essential to diagnosis; for example, headache can have vascular or inflammatory features, but within those categories there are multiple etiologies. Some important classifications are presented in Table 10.1.
Table 10.1 Localization of pain syndromes
| Disorder | Type | Features | Etiologies |
| Headache | Vascular | Migrainous headache with throbbing of steady headache, often associated with nausea and/or photophobia | |
| Inflammatory | Steady pain, often severe, with pain with motion of the neck | Infectious meningitis, encephalitis, neoplastic meningitis | |
| Increased intracranial pressure | Holocephalic pain sometimes with visual disturbance | Tumor, infection, pseudotumor cerebri | |
| Limb pain | Bone origin | Aching pain centered in bony elements often worse with weight-bearing or change in position | Trauma, tumor |
| Muscle origin | Aching and/or cramping pain in muscular area often worse with activation of affected muscle(s) | Trauma, inflammation, | |
| Nerve origin | Lancinating and/or steady pain, usually over a defined cutaneous distribution | Neuropathy from any cause, trauma | |
| Spine pain | Bone origin | Aching or crushing pain worse with weight-bearing and torsion | Arthritis, trauma, tumor |
| Nerve origin | Local pain with radiation in the segmental distribution | Cord or cauda equina compression Nerve root compression | |
| Muscle origin | Steady paraspinal pain worse with standing and movement | Strain, trauma |
Psychology of Pain
Acute and chronic pain have distinct effects on the psychological makeup of patients.
Chronic pain: Chronic pain often produces affective disturbance, anxiety, and/or depression. Psychological response to chronic pain can be an impediment to effective pain management.
Pain without identified pathology: Limitations in diagnostic capabilities may result in misattribution of pain as being of nonorganic origin, but pain in the absence of detectable disease or pain exceeding expected symptoms raises the possibility of a psychological component to the pain.
HEADACHE
Overview
While most headache patients will present in an outpatient setting, headache remains a frequent reason for ED visits. Many times, ED physicians will manage the work-up and treatment of headache, but the neurologist may be consulted for patients with refractory headache, sudden severe headache, atypical features of headache, or those associated with abnormal neuroimaging, focal signs, or seizure.
Evaluation
Primary versus secondary headache: Primary headaches, such as migraine, cluster, and tension headache, are not related to underlying pathology. Secondary headaches are a manifestation of an underlying pathology, such as a tumor, stroke, infection, or other etiology. Features suggestive of secondary headaches should be red flags:
