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Neck Muscles and CSM/DCM

By Timothy Boerger
Reviewed by B.Davies

Neck Muscles and CSM– An Update Part 1 of 2

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​This will be the first of a 2 part mini-series on the properties of muscles in the neck and how they impacts outcomes of surgery. We previously looked at this following an early piece of research from North America.  This series will serve as an update on this research. 


Why was this study conducted?

As outlined previously, the amount of fat found within muscles has been linked to the type of symptoms experienced by patients; including the amount of neck pain and walking ability. This new study was done on a separate cohort of patients than the previous study and included measures of neck strength and other quality of life scales not assessed previously which addresses some weaknesses of the previous study.

How was the study conducted?
This study used MRI imaging to measure the size and the amount of fat in muscles in the neck. Neck strength was measured by clinicians using a hand held force sensor. Several questionnaires were performed to assess function, pain, and quality of life. Importantly, this study used what is called a “cross-sectional’ design meaning it only looks at 1 time point. 

What was discovered?
Larger muscles and larger amounts of lean muscle (i.e. muscle without fat) in the neck were associated with increased strength. (We already knew this in general, but it is good to ensure there isn’t something different about patients with cervical myelopathy). More fat in muscles of the neck was associated with more disability measured by the mJOA. Importantly, neither strength, muscle size, or muscle fat were associated with pain, duration of symptoms, neck disability index, or quality of life in this study.

Why is this important?
Between the previous study linked above and this study, it appears that muscle fat may be a biomarker of disability and function in patients with myelopathy.  Currently there are no biomarkers for myelopathy, which makes it difficult to assess how severe it is or give an idea of how things will develop.  More research will be needed to investigate the usefulness of muscle fat as a biomarker, but given that it can be quantified based on existing widely avaliable imaging techniques, it could enter routine clinical practice quickly.
 

Why could muscle fat relate to the severity of myelopathy?
One reason this is being investigated is that fat infiltrates muscle as a response to nerve injury and disuse. For example, if a nerve is injured the nerve doesn’t tell the muscle to contract as much and it allows more fat to become deposited within the muscle itself. 
    

References

  1. Fortin M et al. Relationship Between Cervical Muscle Morphology Evaluated By MRI, Cervical Muscle Strength And Functional Outcomes In Patients With

Degenerative Cervical Myelopathy. Musculoskeletal Science and Practice. 38; epub 2018: 1-7 

  1. Fortin M, et al. Association Between Paraspinal Muscle Morphology, Clinical Symptoms and Functional Status in Patients With Degenerative Cervical Myelopathy. Spine (PhilaPa 1976). 2016 May 23

Heart Break for Myelopathy

Risk of acute coronary syndrome in patients with cervical spondylosis 
​J.Hamilton

What were the aims of the study?

Various studies in the past have described cervical spondylosis (CS), the degenerative changes in the cervical bones and ligaments contributing to degenerative cervical myelopathy, as associated with increased sympathetic nervous tone[1][2].

The sympathetic nervous system plays a role in controlling blood pressure, heart rate and various other aspects of our cardiovascular health.  But part of its control structure also lies in close proximity to the cervical spine. 

Increased sympathetic activity is known to contribute to increased atherosclerosis and cardiovascular events such as stroke, and myocardial infarction (heart attack)[3]

​The authors noted that no research had been done to link the above statements, if CS does cause increased sympathetic activity, does this logically follow that CS causes an increased incidence of cardiovascular events?
 
With this in mind, the aim of the study was to determine if cervical spondylosis increased the risk of cardiovascular health issues, specifically acute coronary syndrome (ACS), which in common terms is a heart attack.

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The sympathetic nervous system is involved in controlling many of your bodies organ systems. Signals originate from ‘ganlgion’ that lie adjacent to the spine. The ganlgion in the cervical spine are involved in control of the cardiovascular system

How was the study performed?

The authors used a national insurance claims dataset of 22 million people in Taiwan and identified 27,947 patients with CS, they then matched this with a similar number of non-CS patients of a similar age and gender distribution, as well as matching numbers of patients with other health problems such as hypertension, diabetes, asthma and stroke. This was to allow them to compare the incidence of ACS between the groups without other diseases invalidating the comparison. 

All the patients were followed up until they had a diagnosis of ACS, died, or the end of the research period occurred at the end of 2011. After this, the number of ACS events in each group were measured as a rate over the number of “person years”. This being the number of times a diagnosis of ACS was made for every year a patient lived.
 
In this paper, the incidence of ACS was measured as number of ACS/1000-person years. These were then compared between various groups to obtain a ratio, to determine the relative risk of ACS occurring in a person with CS compared to someone without ACS in a similar state of health.


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What were the main findings?

Overall, the study showed that patients with CS were 13% more likely to have an ACS, than patients without CS. This was determined ‘statistically significant’, but in real terms this represents a very small increase from 3.9/1000-person years to 4.27/1000-person years in rates of ACS diagnosis. 

Looking in more detail at the patients with CS, for those with myelopathy the risk was slightly higher, increasing by 20% but interestingly, it seems treatment of CS has an effect in reducing ACS risk:
– 
Patients receiving spinal decompression surgery were less likely to have an ACS (27% reduction)
– Patients receiving rehabilitative therapy were less likely to have an ACS (33% reduction) 

The statistical difference between the form of treatment for CS and reducing ACS risk was not significant.  

​How could cervical spondylosis cause acute coronary syndrome?

This is a good question, and not entirely clear.  The researchers suggested that it may be to do with the sympathetic trunk. The cervical sympathetic trunk consists of collections of nerve cells bodies, called ganglia, aligned along the front of the spine.  The ganglion in the neck are involved in control of the cardiovascular system.  This special group of nerves also connect with the ligaments of the spinal column, such as the posterior longitudinal ligament, and the lining of the spinal cord. Irritation to these structures is thought to cause the sympathetic nervous system to increase its output, for example to fibers in blood vessels around the body, causing them to constrict and causing hypertension, which contributes to a diagnosis of ACS.

What can we take from this study?

This is not the first study to show a relationship between CSM and Cardiovascular health (we have previously described a study specifically looking at high blood pressure), however it is the first to show an increased risk of a heart attack.

There are a number of limitations to this study, and the actually increases in risk are relatively small.  But it adds to the research of CSM and Cardiovascular disease, and once again shows the far reaching impacts of CSM.    

References

Shih-Yi Lin et al. Risk of acute coronary syndrome in patients with cervical spondylosis ​Atherosclerosis 2018

[1]M. Singh, I. Khurana, Z. Kundu, A. Aggarwal, Link of sympathetic activity with cardiovascular risk in patients of cervical spondylosis, Int. J. Clin. Exp. Pathol. 3 (2016) 41e44 
[2]M. Singh, I. Khurana, Z.S. Kundu, A. Aggarwal, Galvanic skin response in pa- tients with cervical spondylosis, IJHSR 6 (2016) 148e152.
[3] N. Marina, A.G. Teschemacher, S. Kasparov, A.V. Gourine, Glia, sympathetic activity and cardiovascular disease, Exp. Physiol. 101 (2016) 565e576,