CIDP can be easy or difficult to diagnosis, depending on how a patient is affected by this disease. Therefore, the types and number of tests a physician needs to obtain to make a diagnosis of CIDP will vary from patient to patient. This article will explore how physicians go about evaluating a person for CIDP.

Determining that a patient has CIDP is important because, in contrast to most types of peripheral nerve disease, CIDP is potentially treatable and symptoms may be reversed with intravenous immunoglobulin (IVIG) or other therapies. It is not always easy to distinguish patients with CIDP from those who have some other type of neuropathy. When evaluating a patient for possible CIDP, the two most important tools are the information obtained by (1) speaking with and examining the patient and (2) studying nerves with a test called an electromyogram (or EMG). If the clinical features and EMG findings are not definitive for CIDP, the physician will need to obtain additional information. Potential options include blood tests, spinal tap, and nerve biopsy.

Certain features are strongly suggestive of CIDP, and, if present, the physician will be very suspicious of CIDP before any testing is obtained. These features include numbness or weakness that came on abruptly and progressed rapidly, weakness affecting the arms and legs in a generalized fashion (meaning that muscle in upper and lower parts of the limbs are weak), asymmetrical numbness or weakness (meaning the left and right sides of the body are not equally affected), numbness or weakness affecting the face, severe balance problems, or absent reflexes (the physician checks reflexes by tapping certain spots on the arms and legs with a rubber tipped hammer). Patients with CIDP can have slowly progressing, symmetrical symptoms with preserved reflexes and little or no weakness. Diagnosing these patients can be tricky because they can look just like patients with any number of other types of neuropathy (such as that caused by diabetes). In almost every patient with CIDP the EMG will be abnormal. However, just as with clinical features, there are some EMG findings that will clearly indicate CIDP whereas other findings may be suspicious for CIDP, but could also be caused by other types of neuropathy. When clinical features and EMG findings are both very suggestive of CIDP, the physician may not need any other information to diagnosis CIDP. If either the clinical features or EMG are not definitive for CIDP, then further testing will be necessary.

In almost every patient with neuropathy physicians will obtain blood tests to look for potential causes or contributors to neuropathy. These usually include tests for certain vitamin deficiencies, diabetes, thyroid problems, and indicators of possible nerve inflammation. However, after EMG, the most valuable tests used to confirm a diagnosis of CIDP are spinal tap and nerve biopsy.

A spinal tap (also called lumbar puncture) involves numbing an area over the lower back with a local anesthetic and, using a needle, withdrawing a tablespoon or two of the fluid that bathes the brain, spinal cord and upper portions of the nerves (called cerebrospinal fluid, or CSF). Although this might sound dangerous and painful, this is a rather safe procedure that can be performed in a physician's office with minimal discomfort and takes less than an hour. An elevated protein level in the CSF is very supportive of a diagnosis of CIDP. The presence of too many white blood cells in the CSF, in contrast, points away from CIDP and suggests certain other nerve diseases that can mimic CIDP. Therefore, spinal tap can be a very helpful test in the assessment of a patient with possible CIDP.

Usually the results from EMG, blood tests and spinal tap, when combined with the patient's clinical features, are sufficient to make an accurate diagnosis. However, if a physician is suspicious of CIDP but the EMG and spinal tap results are not definitive, a nerve biopsy may be performed. This procedure is more involved than a spinal tap, but can also be performed in a physician's office using local anesthesia (sometimes this will be performed in an operating room with the patient asleep using general anesthesia). Usually a nerve called the sural nerve is biopsied. A segment of nerve several inches long is taken from the lower calf or near the ankle. The sural serve carries information about sensation on the outer edge of the foot. In most patients who are undergoing this procedure, there is already numbness in the foot from the neuropathy, so usually no new numbness is appreciated after the biopsy. To get the best results, the biopsied nerve specimen should be processed and interpreted at a facility with the necessary expertise. Not all hospitals have this expertise and biopsy samples are often sent to a specialized nerve pathology lab. Even with appropriate processing and interpretation, a nerve biopsy from a patient with CIDP may be inconclusive. However, in certain circumstances, nerve biopsy can be very useful for confirming the diagnosis of CIDP or indicating an alternate diagnosis.

Hopefully, this article has provided a helpful overview of the types of tests used to diagnose CIDP and the factors that may lead a physician to order a particular test. It should be clear that not all patients will travel the same path to diagnosis.