Proximal Arm Weakness

Proximal arm muscles include supra and infra spinatii, pectoralis major and minor, teres major and minor, rhomboids, serratus anterior, deltoids, biceps, and triceps. The main function of these muscles is to lift the arms. The first sign of proximal weakness is difficulty in raising the arms above a horizontal level. Shoulder conditions like supraspinatus tendonitis are often confused as proximal weakness. In myopathies, usually proximal arm weakness is associated with proximal leg weakness. Motor neuron diseases like ALS and SMA and neuropathies like CIDP may present with symmetrical proximal weakness. For differentiation, EMG/NCS is crucial.