Background: Sparing of the quadriceps muscle has been reported in various myopathies. In multiple sclerosis (MS) and pyramidal syndromes, in general, such a differential involvement of distinct muscle groups has not been described.
Methods: Muscle power was evaluated in 127 patients with chronic pyramidal syndrome caused by MS and 37 patients with acute or chronic paraparesis from other etiologies (mainly cerebro-vascular events).
Results: A striking difference in muscle power of the quadriceps (spared) and the iliopsoas (significantly weakened) was found in the patients suffering from chronic pyramidal syndrome caused by MS. The mean muscle power of the iliopsoas was 1.68 ± 1.1 and that of the quadriceps 4.06 ± 1.4 (P < 0.00005). In the control group, the mean muscle power was 2 ± 1.2 and 2.4 ± 1.4 (difference not significant), for the iliopsoas and the quadriceps, respectively.
Conclusions: Quadriceps muscle remains relatively spared in patients with MS, even with severe and long-standing paraparesis. Various neuroanatomical, neurophysiological, and rehabilitational mechanisms may be involved and explain this phenomenon. This observation may contribute to the building of more reliable and linear scales for the assessment of motor disability and disease progression in MS.