Today’s article will go over Carpal Tunnel Syndrome, Thoracic Outlet Syndrome, Myofascial Pain Syndrome and Double Crush Syndrome.

First, we will briefly review some of the nerves that may be impacted in either carpal tunnel syndrome, thoracic outlet syndrome and myofascial pain syndrome for a better understanding of how and/or why these conditions come to be including a review what is double crush syndrome. 

First, let’s review the brachial nerve.  The nerve roots from our neck interweave in our upper chest (brachial plexus) to form trunks that branch out to form the three major nerves (radial, median, and ulnar) to our arms and hands.  The brachial plexus is the network of nerves that sends signals from the spinal cord to the shoulder, arm and hand. A brachial plexus injury occurs when these nerves are stretched, compressed (known as a “pinched nerve”), or in the most serious cases, ripped apart or torn away from the spinal cord.

According to the Mayo Clinic the most severe brachial plexus injuries usually result from automobile or motorcycle accidents. Severe brachial plexus injuries can leave the arm paralyzed, but surgery may help restore function.

The subclavian arteries are pipes that carry blood rich in oxygen from your heart to your arms and the back of your brain. Subclavian artery disease develops when blood flow is decreased because a section of one of these arteries has become narrow or is blocked. The symptoms that do occur are tied to the area that is blocked. You may experience arm pain or muscle fatigue when using your arms above your head, or doing any activity that demands more oxygen-rich blood flow to the arms.

As per the Mayfield Brain and Spine Clinic, here is a good description:

A diagnostic tools is the electromyogram (EMG), often used in conjunction with nerve conduction studies (NCS). EMG and NCS are used to study the peripheral nervous system (from the spinal cord to the ends of our hands and feet) rather than the central nervous system (the connections within the brain to the spinal cord). The nerve roots from our neck interweave in our upper chest (brachial plexus) to form trunks that branch out to form the three major nerves (radial, median, and ulnar) to our arms and hands.

In the upper limb, there are more than 200 ways a nerve can be pinched from the neck to the fingers. Fortunately, many of these are quite rare. One of the more common scenarios involves pinching in the cervical spine where the nerve root leaves the spinal cord, a condition we call cervical radiculopathy. We have 8 cervical nerves (C1 to C8), but those most commonly pinched are C5, C6, and C7.

Carpal tunnel syndrome is the single most common nerve pinch in the arm and actually occurs in the wrist. In about 10% of carpal tunnel cases, there is also a cervical radiculopathy. It is believed that the pinching of the nerve in one area can predispose the remaining nerve to pinching as well. This is the so-called “double crush,” the pinching of the nerve in two distinct locations, in this case the neck and the wrist.

As it relates to the upper limb, here is a table of the nerves that may be impacted:

Upper Limb

Distal Compression Sites	Proximal Compression Sites
Median Nerve – Carpal Tunnel Syndrome (wrist)	Median Nerve – Pronator Teres Syndrome (forearm) – Cervical Nerve Entrapment (neck) – Thoracic Outlet Syndrome (shoulder)
Ulnar Nerve – Guyon’s Canal Entrapment (wrist)	Ulnar Nerve – Cubital Tunnel Syndrome (elbow) – Cervical Nerve Entrapment (neck) – Thoracic Outlet Syndrome (shoulder)
Radial Nerve – Radial Tunnel Syndrome (elbow)	Radial Nerve – Thoracic Outlet Syndrome (shoulder) – Cervical Nerve Entrapment (neck)

As an example of double crush syndrome, individuals with carpal tunnel syndrome – classically, the median nerve becomes entrapped at the wrist, causing numbness, tingling, weakness and potentially pain into the thumb, index, middle and ring finger. A study conducted in the early 1970s found that 75% of patients with carpal tunnel syndrome also had compression of the median nerve at another site (typically in the neck) which increased the longevity and severity of their pain. [1] It is important to keep in mind the potential of Double Crush Syndrome in patients with suspected nerve compression syndromes as it may contribute to suboptimal response to treatment.

Symptoms are noted as pins and needles, numbness, burning, weakness, pain and lack of sensation. 

We will now review a case that involves these types of pinched nerves.  The case is referenced as MacLeod v Whittemore, 2018 BCSC 1082 (CanLII).

The Plaintiff in this case was quite young, 24 years of age and was involved in a motor vehicle accident in which she injured her neck, back and shoulder.  She was a certified dental assistant and as a result of the injuries she could no longer work in her profession and retraining was required. 

The Plaintiff’s position was that the injury she endured as a result of the collision was Myofacial Pain Syndrome with trigger points in the scalene and pectoralis minor muscles and Thoracic Outlet Syndrome.

The Defendants took the position that the Plaintiff suffered only from Myofascial Pain with trigger points in the left four quarter, left paracervical, pariscapular, and pariclavicular muscles with elbow and wrist and irritability of the left brachial plexus secondary to the above.  The defence expert neurologist was of the opinion that there was no evidence of double crush syndrome which is explained by the fact that during his examination of the plaintiff she did not display any symptoms of  TOS.

The importance in this determination was key because the treatment, depending on what the correct diagnosis was, would be very different and potentially substantial. 

Symptoms:

• numbness in both hands
• pain in the left shoulder
• pain in the left arm, and
• pain in the hand
• Pain radiates down from her left shoulder into her wrist.
• Tenderness in left elbow
• headaches
• insomnia
• difficulty gripping and holding items
• numbness of 4^th and 5^th fingers
• numbness in the left first, second, fourth, and fifth fingers
• pain in left thumb
• sharp feeling down her left arm with movement.
• tenderness to palpation of the plaintiff’s trapezoid and paraspinal muscles, her inner left elbow, and left lower rib area
• psychological injury

Treatments and Medications:

• analgesic medication
• muscle relaxants
• sleep medication
• physiotherapy
• massage
• Feldenkrais Method therapy
• Needle based therapy
• Botox
• good ergonomics
• good posture
• the avoidance of repetitive strain of muscles
• avoidance of repetitive irritation of the nerves
• avoid the repetitive use of the arms at or above chest level especially with the arms away from the chest.

The Plaintiff underwent nerve conduction studies which were normal and vascular TOS studies, that was positive for left sided thoracic outlet syndrome.

Experts/Assessors that were seen by the Plaintiff

• General Practitioner
• Neurologist
• Physiatrist
• Vascular Surgeon
• Plastic surgeon

The Court accepted the opinion that identified the diagnosis of myofascial pain with trigger points, thoracic outlet syndrome and double crush syndrome.  We will enumerate the opinion below in short form:

• the plaintiff has chronic MPS with myofascial trigger points in the scalene and pectoralis minor muscles and post‑traumatic TOS.
• the plaintiff’s symptoms of numbness and tingling are mainly due to brachial plexus irritation at the level of the thoracic outlet.
• found irritability of the ulnar nerve at the level of the elbow
• positive ulnar flexion test which may represent a degree of ulnar nerve irritation in the cubital tunnel.

What is Thoracic Outlet Syndrome?

…it is that condition where the intermittent compression or irritation of the structures which pass from the chest cavity over the first rib and into the arm. This subclavian artery (the main artery to the arm) and the nerves of the brachial plexus (the nerves to the arm) pass between the anterior and middle scalene muscles as they exit over the fifth rib.

What is a Double Crush Syndrome?

Double crush syndrome occurs where there is proximal nerve irritation or injury at the level of the brachial plexus making the distal nerve more susceptible to compression or irritation.

Some of the factors that led to the diagnosis:

• the plaintiff never had the symptoms prior to the accident.
• nerve conduction studies of damage of the ulnar nerve were negative. Therefore concludes that the plaintiff’s sensitivity of the ulnar nerve at the level of the elbow is likely part of a double crush syndrome and a mild ulnar neuropathy but this would not explain all of the numbness and tingling in her arm and fourth and fifth finger.

What is the explanation to the inconsistent test results?

The numbness and tingling is caused by compression of the brachial nerve caused by inflammation of the muscles. If the muscles are not particularly inflamed at the time of testing, it will not result in numbness and tingling in the fingers. Testing may not always yield positive results but that does not mean that the underlying injury is cured or does not exist.

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