Sensory characterization of somatic parietal tissues in humans with chronic fatigue syndrome

Patients with chronic fatigue syndrome (CFS) mainly complain of symptoms in the
musculoskeletal domain (myalgias, fatigue). In 21 CFS patients the deep (muscle)
versus superficial (skin, subcutis) sensitivity to pain was explored by measuring
pain thresholds to electrical stimulation unilaterally in the deltoid, trapezius
and quadriceps and overlying skin and subcutis in comparison with normal
subjects. Thresholds in patients were normal in skin and subcutis but
significantly lower than normal (hyperalgesia) in muscles (P < 0.001) in all
sites. The selective muscle hypersensitivity corresponded also to fiber
abnormalities at muscle biopsy (quadriceps) performed in nine patients which were
absent in normal subjects (four cases): morphostructural alterations of the
sarchomere, fatty degeneration and fibrous regeneration, inversion of the
cytochrome oxidase/succinate dehydrogenase ratio, pleio/polymorphism and
monstruosity of mitochondria, reduction of some mitochondrial enzymatic
activities and increments of common deletion of 4977 bp of mitochondrial DNA
150-3000 times the normal values. By showing both sensory (diffuse hyperalgesia)
and anatomical (degenerative picture) changes at muscle level, the results
suggest a role played by peripberal mechanisms in the genesis of CFS symptoms.
They would exclude the heightened perception of physiological signals from all
districts hypothesized by some authors, especially as the hyperalgesia is absent
in skin/subcutis.