Phrenic neuropathies

Causes:

Cervical spine-- motor neuron disease, poliomyelitis, herpes zoster
Neck-- stab wounds, surgery, anesthetic blocks in the brachial plexus; catheterization of internal jugular and subclavian veins, malignancy.
Chest-- thoracic surgery, mediastinal tumor, or irradiation
Uncertain-- Acute brachial neuropathy, diabetes mellitus, sarcoidosis, Guillian barre, idiopathic.
Muscle--NMJ -- acid maltase, polymyositis, myasthenia gravis

Pearls
1. Zoster is usually unilateral and asymptomatic, with herpetic lesions the tipoff and the chest X ray diagnostic.

2. Brachial plexus anesthesia blocks are usually temporary and asymptomatic, but bilateral blocks are not advisable due to risk of total diaphragm paralysis.

3. Metastases in the neck may also cause Horner's syndrome and the recurrent laryngeal nerve, causing vocal cord paralysis, and may be due to breast cancer.

4. The incidence during open heart surgery ranges from 10-85 % and may be due to ice slurry or topical cooling of heart during surgery. It occurs less often with an insulating pad, but may still occur after pericardiectomy or surgery for mediastinal tumors. In this situation it is often left sided. Bilateral injuries are rare but prolonged ventilator dependence is common.

5. In acute brachial plexopathy, 6 % have phrenic dyfunction and present with shoulder pain and dyspnea. Usually thoracic lesions are excluded and EMG and NCS are helpful.

6. Diabetic phrenic neuropathy is common and may account for the breathlessness of some diabetics.