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 abduct the arms. The first sign of proximal weakness is difficulty raising arms above the 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 (MNDs) like amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) and neuropathies like chronic inflammatory demyelinating polyneuropathy (CIDP) may present with symmetrical proximal weakness. For differentiation, electromyography/nerve conduction study (EMG/NCS) is crucial.