Pyridostigmine Improves Hand Grip Strength in Patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Ella Schlömer^1*Elisa Stein²Claudia Kedor²Rebekka Rust^2,3Anna Brock²Kirsten Wittke²Carmen Scheibenbogen²Laura Kim²

• ¹Institute for Medical Immunology, Charité University Medicine Berlin, Berlin, Germany
• ²Charite - Universitatsmedizin Berlin Institut fur Medizinische Immunologie, Berlin, Germany
• ³Experimental and Research Center (ECRC), Charité-Universitätsmedizin Berlin, Berlin, Germany

Background: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a multisystemic disease characterized by exertional intolerance and fatigue which is often accompanied by muscle weakness and fatiguability. A study showed efficacy of the acetylcholinesterase inhibitor pyridostigmine on cardiac output in ME/CFS patients. Pyridostigmine is currently used off-label in ME/CFS and postural orthostatic tachycardia syndrome. Methods: We evaluated the effect of pyridostigmine on hand grip strength in 20 patients with post- infectious ME/CFS. Hand grip strength testing was performed ten times using an electric dynamometer and was repeated after one hour. In a second test, 30 mg of pyridostigmine was given immediately after the first measurement. Orthostatic function was assessed using a passive standing test. Neurological examination and autoantibody testing were performed to rule out a diagnosis of myasthenia gravis. Results: All patients had reduced maximum hand grip strength with a median of 16.45 kg (IQR: 11.45 kg – 22.8 kg). Hand grip strength was diminished by a median of 4.65 kg after one hour. In contrast, one hour after pyridostigmine administration, patients showed an improvement in maximum hand grip strength with a median increase of 2.6 kg. The maximum hand grip strength after exertion was about 1.5 fold higher with then without pyridostigmine (p = 0.01). The increase in heart rate from lying to standing was median 17 beats per minute without pyridostigmine (IQR: 13 beats per minute – 23 beats per minute) and 13 beats per minute (IQR: 9 beats per minute – 20 beats per minute) (p = 0.017) with pyridostigmine. None of the patients tested positive for myasthenia gravis specific autoantibodies. Conclusion: Pyridostigmine exerts an immediate effect on muscle strength and orthostatic function. This may be attributed to increased acetylcholine availability at neuromuscular junctions, and its augmentation of parasympathetic tone.