Peripheral neuropathy involves damage to the peripheral nervous system, the network of nerves outside the brain and spinal cord. This damage interferes with communication signals traveling between the central nervous system and the rest of the body, leading to a range of symptoms. The condition progresses gradually, with “stages” describing the increasing severity of symptoms. This progression shifts the experience from sensory discomfort to significant functional and physical impairment.
The Onset of Symptoms
The earliest phase of neuropathy often begins subtly and is sometimes disregarded. Symptoms usually start in the longest nerves first, typically affecting the feet and hands in a pattern known as length-dependent polyneuropathy. This initial stage is characterized by mild, intermittent sensory changes known as paresthesia, described as tingling, prickling, or pins-and-needles sensations.
The mild numbness and discomfort are often sporadic, occurring in brief, easily overlooked episodes. Patients may experience occasional shooting or burning pain, a positive symptom where the damaged nerve generates abnormal signals. A frequent early complaint is the feeling of wearing socks or gloves even when the skin is bare, illustrating the initial symmetric sensory disturbance.
Progressive Functional Impairment
As nerve damage continues, symptoms become more consistent and noticeable, moving beyond discomfort to functional impairment. Pain becomes more pronounced and persistent, no longer intermittent. The burning or throbbing pain intensifies, sometimes leading to allodynia—pain caused by normally non-painful stimuli, such as the light touch of a blanket.
Motor nerves begin to show significant damage, leading to muscle weakness and difficulty with coordination. Fine motor skills, such as buttoning a shirt or handling small objects, become challenging as muscle control deteriorates. Loss of sensation and muscle control in the feet contributes to balance issues and an unsteady gait, increasing the risk of falling.
The body’s reflexes may become diminished or absent as the nerve damage progresses, detectable during a physical examination. This combination of increased pain, consistent numbness, and developing muscle weakness significantly disrupts normal daily activities. Symptoms become constant factors that limit mobility and independence.
Advanced Complications and Loss of Sensation
The most advanced phase of neuropathy is marked by severe nerve damage leading to paradoxical outcomes: intense pain may give way to complete numbness (anesthesia). This total sensory loss means the patient can no longer feel pain, temperature, or pressure in the affected limbs, most commonly the feet. This loss of sensation is dangerous because minor injuries can go unnoticed.
Undetected injuries are susceptible to infection, which can spread quickly and lead to non-healing foot ulcers, especially if circulation is compromised. In severe cases, chronic infections can progress to gangrene, sometimes necessitating amputation. Severe motor nerve damage also leads to significant muscle atrophy and can cause foot deformities that further impair mobility.
Autonomic nerves, which control involuntary bodily functions, may also be affected, leading to severe internal complications. Symptoms of autonomic neuropathy include:
- Difficulty regulating blood pressure, causing lightheadedness or dizziness upon standing (orthostatic hypotension).
- Digestive issues, such as bowel and bladder dysfunction.
- Problems regulating body temperature through sweating.
Identifying the Underlying Cause
While the stages describe symptomatic progression, the clinical approach involves identifying the underlying cause and measuring the extent of nerve damage. Causes of neuropathy are varied, including diabetes, autoimmune disorders, vitamin deficiencies, or exposure to toxins. Determining the root cause is necessary to guide treatment and potentially slow progression.
Diagnostic tools confirm the severity and type of nerve damage implied by symptoms. Nerve Conduction Studies (NCS) and Electromyography (EMG) assess the function of large, myelinated nerve fibers. NCS measures electrical signal speed, while EMG assesses the electrical activity of muscles.
Specialized tests are employed for assessing damage to small nerve fibers, which transmit pain and temperature sensations. These include quantitative sensory testing (QST), which measures sensitivity to various stimuli, and skin biopsies. Skin biopsy measures the density of intraepidermal nerve fibers, providing a metric for small-fiber loss.