Overview of Sural Nerve Biopsy
Peripheral neuropathy is a medical condition that affects the nerves outside your brain and spinal cord, often causing weakness, numbness, and pain. There are many different reasons someone may have peripheral neuropathy, but the most common cause is diabetes. About half of the people with diabetes experience some type of peripheral neuropathy.
This condition can also be due to other causes, which can make it difficult to diagnose and treat. Although there are non-invasive tests that can be done to identify this condition, when these are not enough, a sural nerve biopsy becomes a useful tool for possible diagnosis and treatment. A sural nerve biopsy is a medical procedure where a small piece of a nerve in your leg, called the sural nerve, is removed to be examined under a microscope.
This procedure requires careful planning and follow-up to ensure the patient’s safety and to address any possible complications that may arise. Understanding the structure of the nerve, why the biopsy is needed, how the procedure is carried out, what problems could potentially occur, and what kind of follow-up care is necessary after the procedure, are all important parts of making sure a sural nerve biopsy is successful.
Anatomy and Physiology of Sural Nerve Biopsy
The sural nerve is like a messenger that sends feeling information from the outer side of your foot and ankle to your brain. It is made from two branches of outside nerves called the tibial nerve and the peroneal nerve. Near the area where the gastrocnemius muscle, the muscle that forms part of the calf of the leg, begins, a branch from the tibial nerve (the medial sural cutaneous nerve) merges with the lateral sural cutaneous nerve from the common peroneal nerve. This part is typically around where the fibular head, the round top part of the fibula bone in your calf, is located.
Keep in mind that everybody’s body is slightly different, and the nerves may not always be in the exact same place. But, in one study, this was true for about 85% of the bodies they looked at. The sural nerve follows a path down the back and outer side of your leg, diving deep and ending at the outer side of your foot, around the area of your little toe.
During a medical procedure where they need to take a small part of the sural nerve, the surgeon might also come across the lesser saphenous vein. This vein starts near the small toe, goes back and towards the outside (just like the sural nerve!), and ends up between the heads of your calf muscle, where it links with the popliteal vein, the main vein behind your knee.
The sural nerve mainly works to send sensory information like touch, heat, and pain to your brain. However, some studies found that it can have a few small motor fibers, which are responsible for movement. Because the sural nerve is easy to reach, it is often chosen when doctors need to take a small bit of a nerve to study it or use it elsewhere in the body.
Why do People Need Sural Nerve Biopsy
A sural nerve biopsy is a medical procedure where a small piece of your sural nerve (a nerve in your lower leg) is taken out and looked at under a microscope. This is usually done to help diagnose certain conditions that affect your nerves. However, this procedure can cause some health problems, so doctors prefer to use other ways to diagnose these conditions first.
Before even considering a nerve biopsy, your doctor will get a full medical history from you and perform a physical examination. They may also use various tests that measure the electrical activity in your nerves (like electromyography and nerve conduction velocity). If all these tests don’t provide a clear diagnosis, then a sural nerve biopsy might be considered.
Even then, it’s recommended to only have a sural nerve biopsy if certain conditions are met. First, there needs to be evidence that your condition might be something other than diabetic peripheral neuropathy (a common type of nerve damage linked to diabetes). Second, the disease you’re suspected of having should cause visible changes in the nerve that can be seen under a microscope (histopathological changes). Lastly, the results from the biopsy should be able to help your doctor adjust your treatment plan.
There are certain health conditions that might warrant a sural nerve biopsy, but only after all the above steps have been followed. These include vasculitic neuropathy which can be improved with the use of immune system suppressing drugs, nerve damage caused by leprosy, a chronic inflammatory condition called demyelinating neuropathy, inherited nerve diseases, and both acute and chronic axonopathy, which are conditions affecting the nerve fibers. If you’re suspected of having any of these conditions, and other diagnostic methods have failed, then a sural nerve biopsy might be considered.
When a Person Should Avoid Sural Nerve Biopsy
There are certain circumstances where a medical procedure should not be done. These are called absolute contraindications. These include:
If a person has an active infection, it means that their body is currently fighting off an illness caused by bacteria, viruses, or other harmful microorganisms. Doing a procedure during this time can be risky.
Arterial insufficiency is a condition where the blood vessels (arteries) cannot carry enough blood to the body’s organs and tissues. If a person has this condition, a medical procedure might be too dangerous.
The term neuropathy refers to nerve damage or problems. Sometimes, these nerve problems are caused by something else that is more likely the cause. If this is the case, it might not be safe or necessary to do the procedure.
Other conditions or factors may also make the procedure too risky or unsafe.
Equipment used for Sural Nerve Biopsy
A sural nerve biopsy is a procedure where a small sample of your sural nerve (located in your leg) is removed for examination. It’s a straightforward procedure that doesn’t require any special tools. The doctor will use common surgical tools like a scalpel (a sharp knife used in surgeries), retractors (tools that hold open the wound), forceps (tweezer-like tools for picking up small things), and material for stitches.
Microsurgical loupes, which are basically just magnifying glasses, can be used to help the surgeon see better during the procedure. Typically, a tourniquet (a tight band used to control bleeding) is not needed. However, your doctor also has the option to use a bipolar cautery, which is a tool that uses electricity to seal off blood vessels and even control bleeding.
The hospital or lab analyzing the nerve sample should be notified before the biopsy is done. This is because different facilities might have different requirements for how the sample should be prepared.
Who is needed to perform Sural Nerve Biopsy?
The procedure can be done by a range of medical professionals, including general surgeons (who operate on various parts of the body), neurosurgeons (brain and nerve system specialists), podiatrists (foot and ankle doctors), orthopedists (doctors trained in treating bones, joints, and muscles), and more. It is always recommended to have a team of these professionals working together. This way, they can combine their different skills and knowledge for the best patient results.
Preparing for Sural Nerve Biopsy
Before a sural nerve biopsy, a procedure that carries risks, doctors first try all other less risky methods.
Before any procedure, doctors will look at the patient’s medical history and carry out a physical exam. They will specifically check which nerves are affected and how well the patient’s body is still functioning.
Blood tests are a standard precursory step and these can include a complete blood count and comprehensive metabolic panel to see how well the body is functioning. Depending on the suspected diagnosis, the doctor might also order specific tests. If inflammation of the blood vessels in the nerves is suspected, the doctor might test for C-reactive protein and erythrocyte sedimentation rate, both of which are markers of inflammation. If diabetes-related nerve problems are suspected, the doctor may want to check the levels of glucose and hemoglobin A1c in the blood, and also assess kidney function.
To further understand the nerve affected, the doctor could order tests that measure the speed of nerve signals (nerve conduction velocity testing) or advanced imaging like ultrasound or an MRI to visualize the nerve. Other specialists like neurologists or neurosurgeons could be involved in the patient’s care to ensure the best treatment approach.
Lastly, it is essential that patients understand all the risks and benefits associated with the biopsy, and what can be expected after the surgery. This helps manage the patient’s expectations and make informed decisions about going ahead with the procedure.
How is Sural Nerve Biopsy performed
The procedures typically start with the back area of the fibula, which is a bone in your lower leg. For easier access, the patient is placed belly-down. A new method has been recommended to be conducted near the top of the calf muscle to reduce complications during the procedure.
The doctor marks a spot located between your Achilles tendon (a strong tendon at the back of your ankle) and the back end of the fibula bone that is about 2 to 3 inches above the ankle bone. A cut is made and the lesser saphenous vein (a small vein found behind your leg) is identified. The vein is then pulled back so the sural nerve can be seen. The sural nerve is a sensory nerve in your calf.
Depending on the medical condition, the doctor may either take out the whole nerve or just parts of it. If the patient’s symptoms are severe and not all parts of the nerve are affected, it’s suggested to remove the entire nerve for examination. If the symptoms are mild and the disease appears to be in the nerve bundles, then only a part of the nerve should be removed.
If the entire nerve is removed, unstitched strings are placed onto both ends of the nerve and the nerve is cut above these strings. This creates a type of hammock with the string to avoid squeezing the nerve as it’s removed. If only a part of the nerve is removed, similar techniques are used. It’s important that the nerve isn’t squished or coiled during removal and preservation. Depending on the type of lab and its needs, how the sample is stored can vary, hence why it’s necessary to get instructions from the local facilities.
Following the removal of a part of the nerve, the doctor can try to reconnect the remaining nerve structures under a microscope. There are many different products available, such as those made from collagen (a protein found in your skin), that can be used to decrease risks and side effects, and prevent the formation of neuromas (painful, benign growths) after the procedure.
Possible Complications of Sural Nerve Biopsy
A research study was conducted involving 50 patients who had a biopsy (a medical test where tissue is taken from the body to examine it) on their sural nerves (nerves in the back of the leg). The study found that the biopsy results made them change the patients’ diagnosis 14% of the time and changed their treatment plan 60% of the time. Additionally, one third of these patients reported experiencing more pain six months after the biopsy.
However, another small study involving 16 patients found that after the biopsy, all patients did not have any surgical pain. This study also documented that the main complaint from patients, five years later, was a specific type of uncomfortable sensation (called dysesthesias) that seems to be triggered by touch, located in the area where the sural nerve functions.
An 18.4% of patients, who had a biopsy for their whole sural nerve (study involving 717 patients), reported experiencing a decrease in sensation in the area where sural nerve functions. The study also found that the type of biopsy (fascicular – involving a group of nerve fibers, or whole nerve) did not influence the chances of losing sensation.
What Else Should I Know About Sural Nerve Biopsy?
Before conducting a sural nerve biopsy, doctors prioritize thorough preparation, communication with the patient, and consultation with expert pathologists. A sural nerve biopsy is a test where a sample of tissue from the sural nerve, which is located in your lower leg, is taken and examined to identify any problems or diseases. This procedure provides crucial information about the cause of neuropathy, a condition causing nerve damage. Though it may have some complications, the sural nerve biopsy stands as the most effective way in diagnosing specific issues like peripheral nerve vasculitis, a rare disease that causes inflammation and damage to peripheral nerves.
