10-Minute Diagnosis Manual

Paresthesias and dysesthesias are due to dysfunction of the nervous system that can occur anywhere along the pathway of sensation between the cortex and the sensory receptor. Dysfunction can be related to either lack of function (e.g., numbness due to carpal tunnel syndrome) or excess function (e.g., pain from postherpetic neuralgia)(1).

The most common source of paresthesia is peripheral neuropathy. The most common causes in the United States are diabetes and alcoholism. Other common causes include hypothyroidism, vitamin B₁₂ deficiency, postherpetic neuralgia, and nerve entrapments such as carpal tunnel syndrome (2).

The history should include time of onset, duration, and location. Past medical history should be obtained for illnesses that can cause paresthesias or dysesthesias (e.g., diabetes, human immunodeficiency virus [HIV], hypothyroidism, rheumatoid arthritis). Social history may reveal substance abuse (e.g., alcoholism, or intravenous drug use, which would raise the suspicion of HIV) or occupational exposures (e.g., exposure to lead or mercury). In addition, occupational history may reveal an occupation at risk for repetitive motion injuries at work (e.g., a transcriptionist who would be at higher risk for carpal tunnel syndrome). Family history may disclose a hereditary neuropathy (2).

The patient should have a complete physical examination, paying particular attention to the sensory portion of the neurologic examination. Complicating the physical examination is the fact that the examiner must rely on the patient's subjective response to the examination. The examination should test for pain (using a pin or needle), light touch (using a cotton-tipped swab or wisp of cotton), vibration (using a tuning fork), temperature, and position sense (performed with the eyes closed). The examination should delineate the distribution of abnormal as this may be enough to establish a diagnosis. The patient may be asked to map the affected area. Other aspects of the neurologic examination should include testing of muscle strength and reflexes. Muscle wasting may be noted (1,2). Flexion of the patient's neck (Lhermitte's sign) causing electric shocklike pain in the back or extremities may be present in patients with multiple sclerosis, cervical spinal cord disease, or vitamin B₁₂ deficiency.

Initial laboratory work-up should include complete blood count, renal function, fasting serum glucose, vitamin B₁₂ level, urinalysis, thyroid-stimulating hormone, and erythrocyte sedimentation rate. Further laboratory testing might include folate, the Venereal Disease Research Laboratory or rapid plasma reagin test, antinuclear antibody, serum immunoelectrophoresis, purified protein derivative, and blood levels of heavy metals (e.g., lead)(2,3). Electromyography and nerve conduction testing are often helpful in delineating either the anatomic source of the neuropathy (e.g., carpal tunnel syndrome) or the systemic cause (e.g., paraneoplastic syndromes)(3). Radiologic studies such as computed tomography or magnetic resonance imaging may be indicated for specific causes, such as a suspected lumbar disc herniation.

There are several hereditary causes of neuropathies. These include Charcot-Marie-Tooth disease, Denny-Brown's syndrome, and familial amyloidotic polyneuropathy (2).

The differential diagnosis of paresthesias and dysesthesias is broad (see Table 4.6.1).

The cause of paresthesias and dysesthesias can frequently be determined by examination. Distal sensory loss is the most common and is frequently due to metabolic or toxic causes such as diabetes, alcoholism, vitamin B₁₂ deficiency, or heavy metal exposure. Some causes, such as diabetes or alcoholism, can have various clinical patterns. Diabetes most commonly causes a symmetric distal sensory loss, but can also cause multifocal neuropathies, autonomic neuropathies, or even symmetrical proximal motor neuropathies (3).

Most nerve entrapments are distinguished by an examination consistent with their nerve distribution (e.g., loss of sensation of the fifth finger and adjacent half of the fourth finger in ulnar neuropathies, which are usually caused by compression at the cubital tunnel in the elbow).

Dermatomal distributions would point to either a radiculopathy or postherpetic neuralgia. Neuropathies involving the cranial nerves are rare, but may be caused by Guillain-Barré syndrome, diabetes, HIV, or Lyme disease (3).