Evaluation of patients with paramyotonia at 23Na MR imaging during cold-induced weakness.

Abstract

PURPOSE:

To prospectively examine whether sodium 23 (23Na) magnetic resonance (MR) imaging can be used to visualize acute intracellular Na+ accumulation and the effects of specific therapy in patients with paramyotonia congenita (PC).

MATERIALS AND METHODS:

Ethics committee approval and informed consent were obtained. Sixteen patients (four women, 12 men; mean age, 46.7 years +/- 16.7 [standard deviation]) with confirmed PC and 10 healthy volunteers (three women, seven men; mean age, 26.6 years +/- 3) were examined by using a 1.5-T MR system with a 16.8-MHz surface coil. 23Na MR imaging was performed before and after local cooling of the nondominant lower leg and exercising, with experimentally induced weakness scored by a neurologist. The 23Na MR examination was repeated in 13 patients and all volunteers after 3 days and, additionally, in seven patients after 4 days of oral administration of mexiletine, which blocks Na+ channels. The 23Na MR protocol comprised two-dimensional (2D) fast low-angle shot (FLASH), 2D radial, and free induction decay (FID) sequences. The FID data were fitted to a biexponential decay curve to evaluate the slow and fast components of the T2 relaxation time. Fast and slow components were assigned to intra- and extracellular Na+ concentrations, respectively. Radial and FLASH MR images were evaluated by means of a region-of-interest analysis by using 0.3% saline solution for reference. T1- and T2-weighted MR imaging were also performed. Data were analyzed by using a parametric t test.

RESULTS:

After exercising, all patients developed considerable weakness exclusively in the cooled lower leg; no weakness was observed in volunteers. In patients, all 23Na MR images showed a significant increase in 23Na signal intensity in the cooled lower leg (P < .001) in comparison with nonsignificant findings in volunteers. After treatment with mexiletine, cooling and exercise induced almost no muscle weakness and no changes in 23Na MR signal intensity in patients.

CONCLUSION:

23Na MR imaging enables visualization of muscular Na+ accumulation associated with muscle weakness in patients with PC, and effects of specific therapy can be detected.

• Authors: Marc-André Weber, Sonia Nielles-Vallespin, Hagen B Huttner, Johannes C Wöhrle, Karin Jurkat-Rott, Frank Lehmann-Horn, Lothar R Schad, Hans-Ulrich Kauczor, Marco Essig, Hans-Michael Meinck
• Journal: Radiology (Radiology) Vol. 240 Issue 2 Pg. 489-500 (Aug 2006) ISSN: 0033-8419 [Print] United States
• PMID: 16775221 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: RSNA, 2006

Chemical References

• Sodium Isotopes
• Mexiletine
• Sodium

Topics

• Adult
• Case-Control Studies
• Cold Temperature
• Female
• Humans
• Leg
• Magnetic Resonance Spectroscopy (methods)
• Male
• Mexiletine (administration & dosage)
• Middle Aged
• Muscle Weakness (metabolism)
• Muscle, Skeletal (metabolism)
• Myotonic Disorders (metabolism)
• Prospective Studies
• Sodium (metabolism)
• Sodium Isotopes