Learning Objectives
- entrapment of a peripheral nerve leads to numbness, paresthesia, or weakness of a specific pattern
- Treatment may be conservative (e.g. splinting) or surgical
- There are rare exceptions to entrapment (schwannoma etc.)
History
MW, a 52 year old woman, is referred to see you for symptoms of numbness and tingling in her left hand. She is left handed. The symptoms bother her upon waking and after driving her car. She has never injured her left arm, or her neck, and there has been no color change. The symptoms occur daily, and they have been present for the past 5 months. There are no symptoms in the right hand.
She has no allergies to medications. She uses the medications ibuprofen and paroxetine. She has a past medical history of depression.
She does not smoke. She works as a research scientist in a biomedical lab. She has two glasses of wine each week.
There is a family history of trisomy 21 in her younger brother.
Review of systems: no fever, no swelling, no joint pain, remainder of ten system review is negative.
Examination
Her blood pressure is 129/81, her pulse is 74, and her temperature is 97.9 F. She is an alert, healthy lady of normal BMI. Her orientation and memory skills are normal. The pupillary exam is normal. Her eye movements are normal. Her smile is normal. Facial sensation to light touch is normal. Hearing is normal. Shoulder shrug and head excursion are normal. The tongue deviates left and right easily. There is no atrophy of the intrinsic muscles of the hands. Strength of shoulder abduction, elbow flexion, elbow extension, wrist extension, and finger abduction are normal. Reflexes in the biceps and triceps are normal on both sides. There is reduced sensation to pin in the palmar surfaces of fingertips 1, 2 and 3 on the left side only. Tinel’s sign is negative. She has normal cerebellar movements and a normal gait.
Localization and Neuroanatomy
The symptoms of tingling and numbness, with the reduction of pin sensation, are very common for peripheral nerve processes. Unlike conditions of peripheral neuropathy, where multiple nerves are affected, mononeuropathy, which is normally due to peripheral nerve entrapment, often has these symptoms in one specific area. The area should correspond to the sensory area supplied by a peripheral nerve. Physical exam findings may include weakness or atrophy, or sometimes reduced reflexes, along with sensory deficits. In this case, the distribution suits that of the median nerve, either at the location of the wrist, forearm, or rarely, a more proximal location. It is theoretically possible but not likely that hand numbness could be caused by a lesion to the sensory cortex of the contralateral parietal lobe.
Diagnosis
The differential diagnosis for this case is median mononeuropathy of the wrist, ulnar nerve entrapment at the elbow, cervical radiculopathy, brachial plexopathy, or schwannoma of the median nerve proximal to the wrist. The first diagnosis is almost certainly the cause based on this history and exam. It is useful to keep in learn the patterns of peripheral nerve entrapment syndromes.
Peripheral Nerve Entrapment Characteristics
| Nerve | Area of sensory and motor deficits | Common site of entrapment |
| Median nerve | First 3 finger tips, thumb abduction | Median anterior wrist (carpal tunnel) |
| Ulnar nerve | Fingers 4+5, finger flexion, abduction, adduction | Ulnar groove |
| Radial nerve | Posterior medial hand, wrist extension | Posterior humerus (spiral groove) |
| Lateral femoral cutaneous nerve | Lateral thigh surface | Lateral inguinal ligament |
| Common peroneal nerve | Lateral lower leg, dorsum of foot, ankle dorsiflexion | Compression of lateral fibular head |
On exam, a Tinel’s sign can be produced by compression of a piece of irritated peripheral nerve. It is often taught to help diagnose median mononeuropathy, but any nerve may have a Tinel’s sign. This test has a poor sensitivity though, and it is best remembered as a pearl to help understand anatomy and physiology.
Peripheral nerve entrapment may not need confirmation by testing. Incomplete exam findings or indeterminate causes may benefit from testing. Nerve conduction studies (EMG) are the gold standard of testing for these disorders. The test is generally objective and it can be used to monitor severity or progression. Nerves that are entrapped tend to demonstrate focal conduction slowing due to loss of myelin. For some cases, ultrasound or MRI is used to study cause of nerve entrapment.
Treatment
The treatment of peripheral nerve entrapment may be by splinting and therapy, medication treatment for symptoms, and sometimes surgery. For example, wrist splinting at night time is often curative for mild median mononeuropathy. It must be done every night, often for months. For paresthesia symptoms, a medicine like gabapentin or amitriptyline is often helpful. When symptoms do not respond to this treatment, or when the illness is relatively severe, an outpatient surgery is warranted to protect the median nerve from damage and create conditions that will help it to heal. Similar treatment is indicated for ulnar nerve entrapment. It is rare that the other entrapment syndromes require treatment with surgery.
Treatment suggestions for nerve entrapment syndromes
| Nerve | Treatment plan | Treatment Goal |
| Median nerve | Wrist splinting or wrist surgery | Maintain sensation and strength of abductor pollicis brevis |
| Ulnar nerve | Elbow splinting or elbow surgery | Maintain strength within intrinsic muscles of the hand and finger flexors |
| Radial nerve | Avoid compression, assess humerus structure | Repair humerus fracture if present |
| Lateral femoral cutaneous nerve | Weight loss, pregnancy delivery, avoid wearing tight waist bands | Symptom relief |
| Common peroneal nerve | Avoid leg crossing, physical therapy | Avoid falls due to tibialis anterior weakness |
Unlike radiculopathy and neuropathy, blood testing is not normally useful for peripheral nerve entrapment. There are rare cases when multiple nerve entrapments appear, such as in the case of neurofibromatosis, hereditary neuropathy due to pressure palsy, or mononeuritis multiplex. These conditions are quite rare however, and would not be suspected for cases like those described here.
Review Questions
- A patient visits you with symptoms of numbness and tingling on the palmar side of the fingers tips of the thumb, forefinger and middle finger. The cause is probably:
a. compression of the median nerve at the wrist
b. compression of the ulnar nerve at the elbow
c. compression of the radial nerve at the spiral groove
d. compression of the musculocutaneous nerve
e. interosseous nerve entrapment in the forearm - A patient visits you with the complaint of numbness and tingling in the skin of the lateral left thigh. The most likely nerve implicated for these symptoms is:
a. the sciatic nerve
b. the lateral femoral cutaneous nerve
c. the femoral nerve
d. the obturator nerve
e. the inferior gluteal nerve
3. A routine case of carpal tunnel syndrome should be treated with
a. Physical Therapy
b. medications for pain relief
c. wrist splinting at night time
d. carpal tunnel release surgery
e. All of the above