A nerve biopsy is a minor surgical procedure where a small segment of a peripheral nerve is removed for detailed examination in a laboratory. This diagnostic tool investigates the underlying cause of nerve-related symptoms, such as unexplained numbness, pain, or weakness in the limbs. The procedure is typically considered when less invasive methods, including blood tests, imaging scans, and electrophysiological studies, have failed to provide a definitive diagnosis. Analyzing the nerve tissue directly provides valuable insights into the type and severity of nerve damage to help guide treatment decisions.
Conditions Diagnosed by Nerve Biopsy
A nerve biopsy is commonly used to identify or distinguish between various types of neuropathies that affect the peripheral nervous system. This diagnostic method is valuable for conditions where the pathology directly affects the nerve structure. The procedure helps confirm suspected conditions like inflammatory neuropathies, which are often treatable with specific medications.
The biopsy helps diagnose vasculitic neuropathies, such as necrotizing vasculitis, which involves inflammation and damage to the blood vessel walls supplying the nerve. Another indication is the investigation of chronic inflammatory demyelinating polyneuropathy (CIDP), which damages the nerve’s protective myelin sheath. Nerve biopsies confirm the presence of abnormal protein deposits, such as in amyloidosis, or help diagnose genetic or metabolic disorders like Charcot-Marie-Tooth disease. Direct tissue examination also provides evidence for suspected nerve tumors, neurosarcoidosis, or infectious diseases such as leprosy.
How the Procedure is Performed
The nerve biopsy is typically performed as an outpatient procedure, meaning the patient does not need to stay overnight. The most common site for removal is the sural nerve, located near the ankle, because it is a purely sensory nerve and its removal results in minimal functional deficit.
Before the procedure, the biopsy site is thoroughly cleaned and sterilized. A local anesthetic is injected to numb the area, though the patient may feel a brief stinging sensation from the injection. The surgeon makes a small incision, typically two to four centimeters long, isolates the nerve, and removes a small length (usually 1.5 to 3 centimeters) for laboratory analysis. The incision is then closed with stitches, which may be self-dissolving or require removal at a follow-up appointment.
Post-Procedure Care and Recovery
Following the nerve biopsy, a sterile dressing or bandage is applied to the incision site. Keeping the wound clean and dry is necessary to prevent infection, and the patient will receive instructions on changing the dressing. Some incisions are closed with surgical glue, which is waterproof and will peel off naturally.
Rest is important in the immediate 24 hours after the procedure, and keeping the biopsied leg elevated helps to reduce swelling and discomfort. Mild pain at the incision site is expected and can usually be managed with over-the-counter pain relievers such as acetaminophen.
Patients are advised to limit strenuous activity for several days, though light walking may be permitted shortly after the procedure. Full healing typically takes a few weeks, and a follow-up appointment is scheduled to check the wound and discuss the expected side effect of permanent numbness in a small area of the foot.
What Pathologists Look for in the Sample
Once the nerve sample reaches the laboratory, pathologists process and examine the tissue under a microscope for specific microscopic abnormalities. A primary focus is identifying signs of inflammation, such as immune cell infiltration within the nerve or around its blood vessels, characteristic of vasculitis or inflammatory neuropathies. Pathologists also assess the structural integrity of the nerve fibers, looking for damage to the axon or the surrounding myelin sheath.
Findings like demyelination (myelin sheath loss) or axonal degeneration help classify the type of neuropathy. They also examine the tissue for abnormal deposits, such as the amyloid protein seen in amyloidosis.