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Neurogenic PMS Diagnosis

DIAGNOSIS CHARACTERISTICS

The diagnostic process for Neurogenic PMS is pretty much identical to the one for NTOS especially since they often coexist.  To read the full description for diagnosis of NTOS, click here.  The main differences in the diagnostic workup between NPMS and NTOS are outlined below.

Conditions That Can Mimic NPMS

Below is a list of medical conditions that have symptoms which can mimic the symptoms of NPMS.  Many of these conditions are more common than NPMS, and thus should be definitively ruled out before any further steps toward a diagnosis of NPMS are taken.  Most of these conditions overlap with the conditions that can mimic NTOS.  The most notable difference in the list of conditions that can mimic NPMS is cardiac disease and breast disease.  This is due to the likelihood of having chest and/or breast pain with NPMS. To make things even more complex, it is possible for NPMS to coexist with these other conditions meaning that a patient can have both NPMS and one or more of the conditions that can mimic it.  An experienced TOS specialist in combination with specialists in these other conditions will likely be necessary in a scenario where a patient has been found to have both NPMS and another one of these conditions.  Ideally, the specialists will collaborate to confirm all diagnoses and determine a treatment plan for all conditions particularly as to in what order the treatments should occur.

  • Carpal Tunnel Syndrome

  • Cubital Tunnel Syndrome

  • Radial Tunnel Syndrome

  • Cervical Radiculopathy

  • Brachial Plexus Injury

  • Parsonage-Turner Syndrome

  • Rotator Cuff Injury

  • Bicep Tendonitis

  • Complex Regional Pain Syndrome (CRPS)

  • Fibromyalgia

  • Multiple Sclerosis

  • Lymphedema

  • Pancoast Tumor

  • Raynaud’s Syndrome

  • Vasculitis

  • ALS (Lou Gehrig’s Disease)

  • Cardiac Disease

  • Breast Disease

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TESTING

Please click here to go to the NTOS diagnosis page to see a comprehensive overview of the various testing that can be done to rule out other medical conditions.  In addition to the tests listed on that page, some patients being worked up for NPMS will undergo a stress test, EKG, echocardiogram, cardiac enzyme testing, and/or breast imaging to rule out cardiac disease and/or breast disease.

PHYSICAL EXAM

As with NTOS, the physical exam is a very important part of the diagnostic process for NPMS.  Many of the components of the physical exam for NPMS are the same as the physical exam for NTOS.  Below is a list of what is typically assessed during a targeted NPMS physical exam:

  • Resting posture of the patient.  Patients will often have posture where the shoulders are rounded and the head and neck are slumped forward.

  • Range of motion of the arm as well as whether any symptoms are triggered by these movements.

  • Hand grip and strength

  • Hand muscle atrophy

  • Exam of nerves in the lower arm to check for signs of carpal and cubital tunnel.  However, it should be noted that if the explanation for symptoms or physical exam findings is that the patient has multiple nerve compression syndromes of the lower arm such as carpal tunnel and cubital tunnel, then it should be considered that the compression is occurring up at the level of the brachial plexus.

  • Swelling, temperature or color changes of the arm and hand

  • Tenderness of the back of the neck over the cervical spine (may indicate cervical spine disease).

  • Increase in symptoms when tilting the head back or when bending the head down toward the chest (may indicate cervical spine disease).

  • Tenderness and pain when pushing on the shoulder joint (may indicate shoulder soft tissue disease)

  • Shoulder blade winging which can be seen with NPMS but also can be caused by a separate primary nerve injury or entrapment issue.

  • Tenderness or deformity of the collarbone joints

  • Tenderness of the SCM, upper trapezius, and other upper back muscles including muscles surrounding the shoulder blade

  • Tenderness with pushing on the subcoracoid space which is just below where the pec minor attaches to the front of the shoulder along with whether arm symptoms are triggered by this. These findings are unique to NPMS, and this is a very important part of the exam as almost all NPMS patients will have these findings which strongly support NPMS diagnosis.

  • Identification of any signs of NTOS, ATOS, or VTOS.

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PROVOCATIVE MANEUVER TESTING

Please click here to go to the NTOS diagnosis page to see a comprehensive overview of provocative maneuver testing which can be performed.  Patients with NPMS will often respond to those maneuvers in a similar manner to those patients with NTOS.

MUSCLE BLOCK INJECTIONS

It’s important to note that a muscle block and a nerve block are not the same thing.  Generally, any type of block injection involves using some type of numbing agent such as lidocaine.  A nerve block involves injecting lidocaine around a nerve or nerves basically to completely deaden the nerves so that they cannot transmit any signals.  With respect to a brachial plexus nerve block, injecting lidocaine around the brachial plexus will only deaden all the nerves which may provide pain relief along with possibly an entirely numb arm, but it will not provide any NPMS diagnostic information.  Simply numbing all the brachial plexus nerves will not provide any information about what is causing the symptoms.  It just might provide temporary relief.  A muscle block involves injecting lidocaine directly into a muscle which deadens the intramuscular nerves.  The purpose of this is to temporarily interrupt muscle spasm.

Pec Minor Muscle Block  This is equivalent to the scalene muscle block performed for NTOS diagnosis.  Because the pec minor muscle is the main contributor to NPMS nerve compression which often involves muscle tightness and spasm, a good way to test for NPMS is to stop that spasm and see if there is any symptom relief.  Stopping the muscle spasm essentially decompresses the nerves.  This is one of the only diagnostic tests that is specific to diagnosing NPMS as opposed to ruling out other medical conditions.  To ensure precise injection location and for safety purposes, it is performed with ultrasound or other imaging guidance such as MRI.  The lidocaine is injected directly into the pec minor muscle and is typically fast acting within minutes.  Most TOS specialists consider a positive response to the block to be obtaining at least 50% relief in symptoms.  This measurement does not only apply to pain but to any NPMS symptoms such as range of motion, feeling of arm weakness or fatigue, numbness, tingling, discoloration, or cold sensations, etc.  To help the patient with measuring the block response, most clinics will have the patient fill out a pain/symptom diary for a certain number of hours following the block.  Sometimes they will have the patient do some provocative maneuvers both before the block and after the block to see if there is any difference in ability or symptoms that are triggered.  While the block is active, some patients will try to do certain activities that are usually difficult for them or that trigger symptoms to see if they are better able to do them.  Typically, the block only lasts for several hours at most.  A positive block response is a very strong indication that NPMS is the proper diagnosis, and some specialists consider it a high likelihood that the patient will respond to treatment whether it is conservative or surgical.  The scalene muscle block and pec minor muscle block can be performed separately on different days or at the same time.  It really depends on the specialist’s protocol and the diagnostic goal.

However, a positive pec minor block response is not required to make a diagnosis of NPMS.  In addition, a negative pec minor muscle block response cannot rule out NPMS and does not mean that a patient will not respond to either conservative or surgical treatment. Some reasons why a patient with NPMS might not get relief from an anterior scalene muscle block are as follows:

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  • The amount and location of the lidocaine injected might not have been accurate resulting in no spasm interruption or only partial spasm interruption.

 

  • The patient has extensive scarring in the pec minor muscle that makes it less responsive to the lidocaine. The lidocaine stops muscle spasm immediately by causing a complete blockade of the intramuscular nerves within the muscle tissues. If the muscle fibers are very scarred, then that tissue might not fully respond to the lidocaine. In this case, the nerves within the muscle will not get completely blocked so the spasm never really gets stopped. 

 

  • The patient has advanced nerve damage such that even with interruption of the pec minor muscle spasm, the nerve symptoms don’t get relieved.

Botox Injections  Botox injections to the pec minor muscle for NPMS are more typically used as a symptom relief measure than as a diagnostic tool.  However, some specialists do use them to assist with diagnosis.  They are used under the same principle as the lidocaine muscle blocks in that Botox interrupts the muscle spasm and therefore decompresses the nerves resulting in symptom relief.  Botox does not take effect as quickly as lidocaine because it works in a different manner, but if effective, it can last up to 3 months.  There can be different scenarios under which someone might not respond well to the Botox.  Therefore, the same qualifiers apply here as for the lidocaine muscle block, which is that a negative Botox response cannot rule out NPMS, and it does not mean that a patient will not respond to either conservative or surgical treatment.

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PUBLISHED DIAGNOSTIC CRITERIA

In 2016, the top TOS specialists in the United States collaborated to come up with standardized diagnostic criteria for all 3 types of TOS.  It was published in an article in the Journal of the Society for Vascular Surgery.  Below are the published standardized criteria for the diagnosis of NPMS, which is the same as the criteria for NTOS.

Reporting Standards NTOS Diagnostic Criteria
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Illig KA, Donahue D, Duncan A, Freischlag J, Gelabert H, Johansen K, Jordan S, Sanders R, Thompson R. Reporting standards of the Society for Vascular Surgery for thoracic outlet syndrome. J Vasc Surg. 2016 Sep;64(3):e23-35. 

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