pathology: fatty degeneration of muscle / myosteatosis

yoga book / pathology / muskelverfettung

Definition

In parallel with the process of sarcopenia, which occurs without any intervention and results in an annual loss of between 1 per cent and 1.5 per cent of muscle mass (approximately 40 per cent between the ages of 20 and 80 years, of which from the age of 25 approx. 0.5%–1% per annum, and from the age of 50 1%–2% per annum) occurs, in the absence of adequate training stimuli, fatty degeneration (myosteatosis) of the existing musculature also takes place, i.e. an increase in intramuscular fat, the proportion of fat within the muscle. This is clearly detectable by MRI and is due to the fact that, as part of muscle turnover, the precursor cells of muscle cells tend to differentiate into fat cells rather than muscle cells (myocytes) in the absence of training stimuli. These fatty degenerations are considered largely irreversible, which is why prevention and the avoidance or delay of progression are of great importance.

Myosteatosis can be regarded as a contributing factor to frailty (Frailty) because it has many consequences that lead to this condition: muscle weakness, functional limitations, risk of falls, frailty, susceptibility to fractures, and loss of the ability to carry out daily activities. Furthermore, it adversely affects the likelihood of conditions such as cardiovascular disease, metabolic disorders, diabetes mellitus, and even malignant diseases. Conversely, diabetes mellitus and obesity contribute to the development of myosteatosis.

The outcome for stroke patients (ischaemic apoplexy) as measured by neurological scales (the National Institutes of Health Stroke Scale (NIHSS) and the modified Rankin Scale (mRS)) depends on ALM (appendicular lean muscle mass) and the degree of myosteatosis (reference: segment C3–C4).

Goutallier classifies myosteatosis into four grades for assessment by CT:
Grade 0: no fat content
Grade 1: low fat content
Grade 2: fat content < muscle content
Grade 3: fat content = muscle content
Grade 4: fat content > muscle content

Myosteatosis must be distinguished from sarcopenic obesity, in which the subcutaneous adipose tissue is increased, whilst the intramuscular fat content is not necessarily increased.

Furthermore, sarcopenia is not the same as myosteatosis; on the contrary, sarcopenia can be described as a quantitative loss of muscle mass, whilst myosteatosis is a qualitative loss of muscle mass. There are currently nine different definitions of sarcopenia, taking into account the following parameters

  1. ALM
  2. Loss of muscle mass associated with a decrease in strength and speed


In one study (involving 445 older adults aged 65 and over), these two were the only factors found to be valid predictors of the incidence of falls. The definition based on the ALM appears to be the more valid one, as it excludes irrelevant factors such as the patient’s motivation and their form on a given day. For men, the link between a lower ALM and an increased risk of hip fractures has been clearly demonstrated; for women, the evidence from studies is inconclusive.
It is also known that sarcopenia is often associated with myosteatosis. In this condition, both the number of muscle fibres and their cross-sectional area decrease, and the number of innervating neurons also declines.

Myosteatosis is a poor indicator of muscle strength: in principle, even a muscle with a small amount of fat can exhibit low maximum muscle strength.

A lack of training stimuli and a tendency to take it easy or avoid certain activities following injuries are likely to be the main causes of myosteatosis. In the region of the spine, the multifidus is particularly well known as a key deep stabiliser for the muscular stability of the spine, and its fatty degeneration is a major cause of various chronic back conditions such as disc herniation (disc protrusion and herniation), spondylolisthesis and spinal canal stenosis. In addition to a lack of stabilisation and a decline in strength and performance, the afferent and efferent flow of information to and from the CNS also deteriorates. This, too, can contribute to chronic pain. Multifidus dysfunction leads to degeneration of the intervertebral discs and associated secondary disorders, as well as to disorders of the facet joints, including osteoarthritis. As is the case in other contexts, a disturbance in the active components of a subsystem inevitably leads, possibly with a delay, to disturbances in the passive components (and vice versa). Improving the muscular condition generally leads to an improvement in pain symptoms.

In a study involving nearly 9,000 patients over an average follow-up period of 9 years, patients with myosteatosis had a 55 per cent increased risk of death; this is therefore roughly comparable to the risk associated with obesity or diabetes mellitus. This figure was independent of the presence or absence of obesity or BMI. In another study, a significant association was found in underweight patients (BMI below 18.5) between myosteatosis and the occurrence of post-operative complications and severe post-operative complications. In colorectal cancer patients, there is a significant association between both myopenia and myosteatosis and a higher ASA classification (perioperative risk). In a cohort of patients who had undergone surgery for Crohn’s disease, an association was found between anaemia and myosteatosis; the same was true for patients with pancreatic cancer. Both adverse body composition (body composition), which also encompasses myosteatosis, and reduced muscle mass (sarcopenia) are associated with poorer overall survival (OS), greater chemotherapy toxicity and more surgical complications in cancer patients.

In general, fatty degeneration can also occur in tendons, where it is referred to as tendolipomatosis.

Cause

  1. Immobilisation
  2. lack of training stimuli
  3. neurological disorders
  4. Underlying conditions affecting the nerves or muscles
  5. Supply disruptions

Predisposing

  1. Sarcopenia
  2. conditions that impair mobility, such as RA

Diagnosis

  1. Computed Tomography / Magnetic Resonance Imaging

Symptoms

  1. reduced muscle strength and performance
  2. limited muscular endurance
  3. muscle pain, if any
  4. fatigue, if applicable
  5. muscle cramps, if any
  6. muscle wasting, if applicable
  7. secondary joint problems (complication), if any
  8. Depending on which muscles are affected: breathing difficulties, difficulty swallowing, speech disorders, heart problems…

Complications

  1. increased risks of various diseases,
  2. increased intra- and post-operative risk
  3. elevated ASA grade
  4. Joint disorders
  5. reduced life expectancy
  6. Osteopenia/Osteoporosis

Therapy

  1. Physical training to prevent or delay the progression of myosteatosis and to build and increase effective muscle mass

DD

Symptoms may vary depending on the muscles affected; therefore, only a few important differential diagnoses will be mentioned here.

  1. Sarcopenia
  2. Frailty-Syndrom
  3. Metabolic syndrome
  4. Muscular dystrophies
  5. Myositis (polymyositis, dermatomyositis, inclusion body myositis)
  6. Cachexia in cancer
  7. Chronic organ failure (heart failure, liver cirrhosis, chronic kidney failure)