Distribution of extremity muscle weakness in myasthenia gravis: sparing of tibialis anterior muscle.

We evaluated the distribution of muscle weakness in 70 myasthenia gravis (MG) patients, using the MRC scale. Extensors in the upper extremities and proximal flexors in the lower extremities (LE) were found to be weak. Tibialis anterior muscle was rarely affected and only when there was substantial weakness in LE proximal muscles. Attention to this distribution may help in differentiating MG, particularly MG with only limb weakness, from muscular dystrophies.