An easy approach to evaluating peripheral neuropathy
Ask what, where, when, and in what setting to narrow your search.
You may test temperature sensation by warming or cooling the handle or prong of the tuning fork and applying it to the patient’s skin.
Joint position testing is performed by asking the patient to avert his eyes, then moving the distal phalanx of a finger or toe up or down by small increments and asking the patient to tell you the direction of movement. Assess a patient’s casual and tandem gait for unsteadiness or ataxia.
Motor symptoms: Weigh them against sensory findings
Most patients with neuropathy have some degree of weakness, but it is usually overshadowed by sensory complaints. Distal lower extremity weakness may manifest as “foot drop,” which, if it affects ankle dorsiflexion, may cause a “slapping” or noisy step due to the forefoot hitting the ground with abnormal force.
Distal upper extremity weakness may cause trouble with fine motor skills of the hands.
Proximal weakness may present as difficulty in rising from a chair or lifting objects above the shoulders.
There may be muscle atrophy or fasciculations.
Motor symptoms are seldom the sole complaint. When motor and sensory symptoms are combined, it is helpful to rank them in order of symptom predominance—ie, motor greater than sensory, or vice versa. For instance, many immune-mediated disorders, such as Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), produce chiefly motor abnormalities and fewer sensory symptoms. Sensory complaints predominate in many other polyneuropathies, especially the “length-dependent” polyneuropathies (ie, those affecting the longer nerves initially) caused by metabolic or toxic disorders.
Autonomic symptom evaluation
The number of processes that affect both autonomic and somatic nerves are relatively few (TABLE 1).5,7,10 It is particularly important to assess symptoms suggesting involvement of the autonomic nervous system.
Autonomic symptoms include lightheadedness, syncope, diarrhea, constipation, postprandial bloating, early satiety, urinary complaints, erectile dysfunction, abnormal or absent sweating, and dry mouth and eyes. Many of these complaints are common in the general population, so their relevance should be based on severity and temporal evolution, as well as comorbidities and medication use.
When complaints do not clearly implicate pathology in the autonomic nervous system, autonomic testing may be helpful, targeted for the domain that may be impaired. For example, bedside orthostatics or tilt-table testing are used for pre-syncopal symptoms, but gastric emptying testing can assist the evaluation of complaints of early satiety or postprandial bloating.
TABLE 1
Relatively common acquired polyneuropathies with autonomic nervous system involvement
| Diabetes mellitus |
| Amyloidosis |
| Guillain-Barré syndrome |
| Paraneoplastic neuropathy (usually small cell lung cancer) |
| Sjögren’s syndrome–associated neuropathy |
Where: The distribution of nerve involvement
“Where” refers to distribution of nerve involvement 1) globally throughout the body and 2) locally along the nerve(s). During the history taking and examination, determine the nature of general distribution (eg, symmetric or asymmetric) and where along the length of the nerve(s) (proximal and/or distal) the dysfunction exists.
Polyneuropathy most commonly presents in a “length-dependent” distribution, with clinical features appearing initially most distally and symmetrically (ie, in the feet). Asymmetry and involvement of the proximal parts of a nerve are “red flags” for an uncommon cause that may require referral to a neurologist (FIGURE).
Comparative vs absolute measurements. At bedside, 2 approaches are used to assess the distribution of nerve involvement: comparative and absolute. The comparative approach searches for a relative difference in sensory thresholds or weakness between sites. It can assess side-to-side or one nerve (or root or region) territory to another. It is useful for establishing sensory or motor impairment in a radicular, plexus, or single nerve distribution.
Testing for an absolute reduction in sensation (eg, decreased vibration in the toes) can be more challenging because it requires experience in judging what is normal and abnormal according to expectations for a particular site and modality. Take into account that sensory thresholds are normally increased with the patient’s age and height.11 For example, we commonly encounter elderly patients whose vibration sensation in the toes is said to be decreased, when in fact the reduced sensory threshold is only an age-related change.
Most assessments of sensory thresholds use the absolute approach because most generalized polyneuropathies are “length-dependent.”
Perform motor testing for appendicular (upper and lower extremities) and axial (neck and trunk) muscles, assessing particularly for weakness, atrophy, and fasciculations.
The typical polyneuropathy caused by metabolic, toxic, inherited, or unknown causes is distal and symmetric.12 Neuropathies caused by other mechanisms, such as immune-mediated or infectious, are rarely length-dependent. Examples include motor neuronopathies (eg, amyotrophic lateral sclerosis), sensory neuronopathies (eg, paraneoplastic), polyradiculoneuropathies (Guillain-Barré syndrome, CIDP), and mononeuritis multiplex (caused by vasculitis).
