How Is Neuropathic Pain Diagnosed?
It is impossible to prove someone is in pain, because pain is a subjective perception. The pain doctor is obligated to believe his or her patient, however, and to devise strategies to manage it. It is more helpful, however, for the doctor to understand what is going on in a patient’s pain syndrome than to label it with a diagnosis.
The Patient History
A history and physical exam are the initial diagnostic tools. The doctor will learn when the pain began, where it’s located now, and its progression, nature, and severity. It can be used to note changes due to pain, such as in skin, hair, nails, skin color, sweating, temperature changes, and muscle spasm. The pain itself requires a specific list of questions whose answers are helpful in understanding the pain:
- Frequency of pain: is it intermittent or continuous?
- Where is the pain located and does it radiate to other areas?
- What is the quality of the pain–burning, tingling, shooting, crushing, stabbing, etc.?
- What makes it better? What makes it worse?
- How has it changed life at home, in a marriage or relationship, in employment?
- Are there any medical conditions that make neuropathic pain more likely, such as diabetes? Herpetic outbreaks–simplex or zoster (shingles)? Previous stroke or closed head injury?
- How has it affected the patient besides its discomfort–depression, anger, or hopeless?
The Analog Pain Score
Pain is known as the 5th vital sign, after temperature, pulse rate, respiratory rate, and blood pressure. A patient will be asked to assign a number to pain severity, 0 being absent and 10 being the worst conceivable pain. This is helpful in determining the urgency of management and as an interval score in judging the success of any treatment.
The Physical Exam
The physical exam incorporates a neurological assessment that attempts to find a cause for the neuropathic pain. Since most neuropathic pain is of a mysterious origin, physical findings are often unhelpful. An evaluation of normal nerve function is limited to a check of reflexes and perception of pinpricks or other tactile testing devices. A previous stroke may only become known by the neurological findings sought when evaluating a patient for neurologic pain. Any damage to the brain can alter pain perception, the dampening process, or the psychological impact to pain’s perception.
Muscle spasm is a frequent condition associated with neuropathic pain, as patients will overtax muscles used to splint away from the painful area, overwhelming their capacity. This causes muscles to become acidotic which results in painful cramping. Occasionally the muscle spasm is so painful that the patient seeks help for it instead of the neuropathic pain that has caused it.
Occasionally, the path of a painful nerve tract can demonstrate small lumps of inflammatory nerve along its path, called trigger points. These are especially sensitive but can be used to advantage by injecting them with anesthetic or just in breaking them up by the needle alone.
Blood tests are indicated with neuropathic pain to identify any underlying conditions that make it more likely, such as diabetes (fasting glucose or hemoglobin A1c level) and rheumatic arthritis (RA factor–rheumatoid factor, C-reactive protein–CRP, erythrocyte sedimentation rate–ESR).
Drug testing is required when patients are on chronic pain medications. Drug diversion is a serious problem resulting in an overdose crisis, and pain doctors will screen their patients to assure the medication prescribed is being taken and that no unprescribed medications or illicit drugs (cocaine, methamphetamines) are being taken. This is not for strictly legal reasons, but for legitimate care of those in whom addiction and dependence may have influenced their behavior and put them in danger.
X-rays, ultrasound, CT, and MRI are used to focus on a limb with chronic neuropathic pain, but are also used to identify any structural conditions (nerve compression) or masses (benign and malignant tumors) that may be causing chronic pain.
- Nerve conduction studies can determine if the signal is traveling through the nerve normally, whether it is delayed, or whether the signal is weak or amplified.
- Electromyography is used to evaluate the electrical activity of muscle fibers innervated by nerves to determine whether the pain is primarily a nerve disease or a muscular disease. It is especially helpful in assessing muscle spasm.