Sarcopenia is defined as a slowly progressive loss of diffuse muscle mass and strength with age. It is the visible part of genuine neuromuscular disease in almost 35% of people over 65 with muscle weakness or elevated CPKs. Type 2 myotonic dystrophy (DM2) and inclusion myositis (IBM) seem to be particularly frequent neuromuscular pathologies in this population and are probably underdiagnosed there.
A German team, based on the description of four emblematic cases of sarcopenia, IBM, DM2 and amyotrophic lateral sclerosis (ALS), aged 85, 80 and 65 respectively, underlines, in an article published at the end of June 2021, the importance of looking for neuromuscular disease behind atypical muscle symptoms of sarcopenia.
The existence of an asymmetry of the deficit and / or a focal deficit should require repeated dosing of CPKs. A rapid rate of change favors an SLA. Being overweight is more common with DM2, while weight loss and undernutrition are readily found with ALS or IBM.
In the presence of high iterative CPKs, performing an electromyogram (EMG) can point to neuropathic or myopathic involvement, DM2 (electrical myotonia), ALS (fasciculations, etc.).
If the EMG is not informative, a muscle biopsy should be considered which will provide evidence for inclusion myositis, DM2 or other muscle pathology.
Finally, a genetic diagnosis (especially looking for DM2) should be considered and treatment by a center specializing in neuromuscular diseases is recommended.
