In the case of scuba and surface supplied divers, the diver breathes gas at ambient pressure, and if this is not able to escape freely during ascent, the pressure difference will cause it to expand, and may rupture the lung tissues (pulmonary barotrauma), and escape to a variety of places, one of which can be the mediastinum. A diver with symptoms of mediastinal emphysema may also have any combination of arterial gas embolism, pneumothorax and subcutaneous or pulmonary interstitial emphysema. Factors which may prevent free escape of the compressed breathing gas include holding the breath or respiratory obstructions such as cysts, mucus plugs, or scar tissue.In rare cases, pneumomediastinum may also arise as a result of blunt chest trauma (e.g. car accidents, fights, over pressure of breathing apparatus), while still evolving in the same fashion as the spontaneous form.Pneumomediastinum is most commonly seen in otherwise healthy young male patients and may not be prefaced by a relevant medical history of similar ailments. Diagnosis
Pneumomediastinum is uncommon and occurs when air leaks into the mediastinum. The diagnosis can be confirmed via chest X-ray showing a radiolucent outline around the heart and mediastinum or via CT scanning of the thorax. Treatment
The tissues in the mediastinum will slowly resorb the air in the cavity so most pneumomediastinums are treated conservatively. Breathing high flow oxygen will increase the absorption of the air. If the air is under pressure and compressing the heart, a needle may be inserted into the cavity, releasing the air.
People with distal axonopathies usually present with sensorimotor disturbances such as amyotrophic lateral sclerosis
Myelinopathy, is due to a loss of myelin or of the Schwann cells. This demyelination slows down or completely blocks the conduction of action potentials through the axon of the nerve cell (neurapraxia). The most common cause is acute inflammatory demyelinating polyneuropathy AIDP, the most common form of Guillain–Barré syndrome (although other causes include chronic inflammatory demyelinating polyneuropathy )
Neuronopathy is the result of issues in the peripheral nervous system (PNS) neurons. They may be caused by motor neurone diseases, sensory neuronopathies, toxins, or autonomic dysfunction. Neurotoxins such as chemotherapy agents may cause neuronopathies. Signs and symptoms
Among the signs/symptoms of polyneuropathy, which can be divided (into sensory and hereditary) and are consistent with the following:
Sensory polyneuropathy – ataxia, numbness, muscle wasting and paraesthesiae. Hereditary polyneuropathy – scoliosis and hammer toes

Causes
The causes of polyneuropathy can be divided into hereditary and acquired and are therefore as follows:
Inherited -are hereditary motor neuropathies, Charcot–Marie–Tooth disease, and hereditary neuropathy with liability to pressure palsy
Acquired -are diabetes mellitus, vascular neuropathy, alcohol use disorder, and vitamin B12 deficiency

Pathophysiology
In regard to the pathophysiology of polyneuropathy, of course, the former depends on which polyneuropathy. For instance in the case of chronic inflammatory demyelinating polyneuropathy, one finds that it is an autoimmune disease. Here, T cells involvement has been demonstrated, while in terms of demyelination, antibodies alone are not capable.