see also Idiopathic brachial plexus neuropathy.
When the etiology is unclear, check CXR (with apical lordotic view), glucose, ESR, and ANA.
If no improvement by ≈ 4 weeks, obtain MRI of the plexus (idiopathic brachial plexitis will usually start to show some improvement by this time; therefore tumor should be ruled out if no improvement).
1. Pancoast syndrome or Pancoast tumor AKA superior sulcus tumor. Clinical: various combinations of pain in the shoulder radiating into the upper extremity in the ulnar nerve distribution from involvement of the lower brachial plexus, atrophy of hand muscles, Horner syndrome , UE edema.
Etiologies:
a) neoplasms:
● most common: bronchogenic cancer, usually non-small cell (NSCLC) (squamous cell or adenocarcinoma) arising in the pulmonary apex
● metastases
b) infections
c) inflammatory: granulomas, amyloid
2. (idiopathic) brachial plexitis AKA neuralgic amyotrophy: most commonly upper plexus or diffuse
3. cervical rib
4. viral
5. following radiation treatment: often diffuse
see Radiation induced brachial plexus neuropathy
6. diabetes
7. vasculitis
8. inherited: dominant genetics
9. trauma