It’s hard to imagine suddenly losing sensation or muscle function or having extreme nerve pain occur without reason. Unfortunately, some nerve injuries or nerve abnormalities can happen without warning. Nerve palsies are rare but can be debilitating. Generally, nerves are injured due to a specific incident, such as a fracture or dislocation. However, nerve palsies can occur spontaneously and the cause is unknown at times. Nerves commonly affected by a spontaneous nerve palsy are the peroneal nerve, brachial plexus, suprascapular nerve, and lateral femoral cutaneous nerve.

Peroneal nerve palsy, or common peroneal nerve entrapment, is the most common spontaneous nerve palsy of the lower limb. The common peroneal nerve travels around the neck (upper end) of the fibula (small outer lower leg bone), where it is very vulnerable to injury. The nerve can be stretched or cut with an injury to the lower leg. The nerve supplies the muscles that raise your foot and toes as well as providing sensation to the top of your  foot. This nerve can become entrapped without any antecedent trauma resulting in weakness to the muscles that raise the foot and toes (resulting in “drop foot”) and numbness on the top of the foot. The reason for developing entrapment is usually unknown. An MRI of the knee is typically obtained to rule out a mass that could be impinging the nerve. An MRI of the lumbar spine may also be obtained to rule out a herniated disc pinching the nerve roots that supply the peroneal nerve.  Physical exam tests include assessing motor and sensation of the nerve. With palpation of the common peroneal nerve, patient’s often have a “zing” type sensation down the outer aspect of the lower leg onto the top of the foot. Treatment of peroneal nerve palsy can range from conservative treatment of rest and observation to surgical intervention. Surgery usually involves decompressing the nerve. As long as the nerve has not been entrapped for months and months which can cause irreversible damage, the surgically decompressing the nerve is typically successful in solving the problem.

Another spontaneous nerve palsy is Parsonage-Turner Syndrome (PTS). This syndrome can affect any nerve within the brachial plexus, a network of nerves that supplies nerve fibers to the upper extremity and shoulder. PTS is a rare syndrome that usually affects only one shoulder, is very abrupt in its nature, and increases quickly with severity of pain. Pain is severe and over the course of days to weeks, the patient will also start to have issues with weakness, reflex changes, and sensory deviations. The syndrome is self-limiting, with pain lasting around 2 weeks with weakness lasting for approximately a month.

Another nerve palsy affecting the shoulder, is suprascapular nerve palsy. This nerve provides function to the supraspinatus and infraspinatus muscles, which comprise half of the rotator cuff musculature. Palsy to this nerve will not only cause pain but can affect the strength of these muscles. Specifically, this can cause weakness when trying to bring the arm away from the body as well as rotating the arm outward. Diagnosis can be confirmed with a special study called electromyography (EMG) or an MRI, although history and physical exam alone can be definitive. Treatment consists mainly of rest, observation, and pain control unless there is something compressing the nerve. In some cases, patients suffering from a labral tear in the shoulder joint can develop a cyst filled with fluid that compresses the nerve. In these cases, the cyst needs to be decompressed and the labrum repaired arthroscopically.

Lateral femoral cutaneous nerve palsy, also known as Meralgia Paresthetica (MP), affects sensation along the outer aspect of the thigh. Pain is usually the most common complaint with this type of nerve palsy. MP can be caused by mechanical compressions from obesity, tight clothing, muscle spasms as well as from metabolic issues such as diabetes and alcoholism. Patients complain of burning, numbness, muscle aching, or a “buzzing” within the nerve region. Pain can range from mild to severe and can improve spontaneously.  Diagnosis is usually one of exclusion. Pain located within this region of the thigh is often due to lumbar spine pathology, so this needs to ruled out first. There are both non-surgical and surgical treatments for lateral femoral cutaneous nerve palsy. Conservative treatment options include NSAIDs, physical therapy, pulsed radiofrequency ablation, and nerve blocks. Surgical options include decompressing the nerve or resecting it altogether. Surgical resection of the nerve would leave a patient with a an area of permanent numbness on the lateral thigh, but the pain usually resolves completely.

Spontaneous nerves palsies as a whole are still somewhat misunderstood. Pain and loss of function continue to be the mainstay of symptoms. Fortunately, treatment options are continuing to improve. This article originally appeared in Vail Daily’s “Ask a Vail Sports Doc” column written by Gretchen Maedor, PA.