Investigating the Triceps Surae in Chronic Inflammatory Demyelinating Polyneuropathy Patients using Magnetic Resonance Imaging

Abstract

IntroductionChronic inflammatory demyelinating polyneuropathy (CIDP) is an acquired autoimmune disease, primarily characterized by peripheral nerve demyelination. Patients present with sensory and motor deficits, including but not limited to symmetrical diffused muscle weakness. Studies to date have mainly focused on the neuropathic aspects of CIDP and its involvement in paresis. Impairments in skeletal muscle quality and quantity may be a consequence of motor nerve deficits, but these aspects have not been investigated comprehensively. Thus, the purpose of this study was to use magnetic resonance imaging (MRI) to explore anatomical and functional differences in the triceps surae muscle complex in a group with CIDP with a healthy control group.MethodsTo date, five patients with CIDP and six healthy control subjects were matched on anthropomorphic characteristics. Both groups underwent isometric plantar flexion strength measurements on a custom dynamometer. On separate days, MRI (T1 and T2) of the leg musculature was acquired via serial axial plane scans in a 3.0‐Tesla magnet. All MRI scans were analyzed using OsiriX imaging processing software. Total muscle volume was computed using the T1 weighted anatomical images with a 3D FLASH sequence: (0.9mm slice thickness with slice separation of 1mm ranging from 280 to 400 slices). T2 weighted relaxation times were determined from images with a spin‐echo sequence (5.0mm slice thickness; 16 echoes between 13.2–211.2ms). Both total volume (T1) and relaxation times (T2) were calculated separately for the three components of the triceps surae: soleus, medial gastrocnemius (MG), and lateral gastrocnemius (LG).ResultsCIDP patients had ~34% less plantar flexion strength compared with controls. CIDP patients had ~14%, ~28% and ~38% smaller muscle total volumes in the soleus, MG and LG, respectively, compared to controls. When strength was normalized to total triceps surae volume it was ~26% lower in CIDP. T2 relaxation times were significantly longer in CIDP with the soleus, MG and LG showing ~37%, ~31% and ~29% longer relaxation times, respectively.ConclusionCIDP patients were significantly weaker compared to control subjects. When strength was normalized to total triceps surae volume the difference remained indicating CIDP patients have lower intrinsic muscle contractile quality. This is further reinforced by the significantly longer T2 relaxation times, which likely reflects an increase in intramuscular fat infiltration in the CIDP group. The results indicate that muscle quantity and quality are affected by alterations in axonal function due to CIDP.Support or Funding InformationSupported by NSERCThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.