Parsonage-Turner syndrome
Toxic neuropathy
Progressive neuropathy secondary to exposure (lead, mercury, heavy metals, chemical solvents)
See weakness, numbness
Traumatic/Acute:
Shoulder Dislocation
Anterior shoulder dislocation
Posterior shoulder dislocation
Inferior shoulder dislocation
Clavicle fracture
Humerus fracture
Scapula fracture
Acromioclavicular joint injury
Glenohumeral instability
Rotator cuff tear
Biceps tendon rupture
Triceps tendon rupture
Septic joint
Anterior shoulder dislocation
Posterior shoulder dislocation
Inferior shoulder dislocation
Nontraumatic/Chronic:
Rotator cuff tear
Impingement syndrome
Calcific tendinitis
Adhesive capsulitis
Biceps tendinitis
Subacromial bursitis
Cervical radiculopathy
Refered pain & non-orthopedic causes:
Referred pain from
Neck
Diaphragm (e.g. gallbladder disease)
Brachial plexus injury<unk> 
Axillary artery thrombosis
Thoracic outlet syndrome
Subclavian steal syndrome
Pancoast tumor
Myocardial infarction
Pneumonia
Pulmonary embolism
Neck
Diaphragm (e.g. gallbladder disease)<unk>
Rucksack paralysis
Parsonage-Turner syndrome
Tick paralysis
Toxic neuropathy
Meralgia paresthetica
Progressive neuropathy secondary to exposure 
Horner syndrome
See weakness, numbness