Decompression sickness

Caisson disease is an uncommon diving-related decompression illness that is an acute neurological emergency, that typically occurs in deep sea divers. 

Diving-related decompression illness is classified into 2 main categories ³:

1. arterial gas embolism secondary to pulmonary decompression barotrauma
2. decompression sickness (Caisson disease), which can be further clinically subdivided into:
   1. mild symptoms: arthralgia, skin marbling, small patchy hemorrhages, and lymphatic obstruction.
   2. serious and life-threatening symptoms: these affect the brain, spinal cord, inner ear and lung.

Pathology

Nitrogen gas bubbles cause can cause neurovascular infarction of the brain and spinal cord leading to neurological deficit. There are various theories to explain this, which hypothesise between arterial occlusion, venous infarction and cellular nitrogen toxicity.

Location

The white matter tracts of the spinal cord and brain are predominantly affected due to their high myelin content ³. Cord lesions are more common than brain lesions. In the spinal cord, there is a predilection for the thoracic cord segments to be affected, thoughthought to be secondary to more nitrogen accumulating in the lateral and posterior columns where there is higher fat content and also the relatively low blood flow compared to the cervical and lumbar segments.

Complications

• bone infarction
• spinal cord infarct

Radiographic features

MRI

Radiological changes are seen in early stages in MRI, but have very low specificity. The affected white matter may show ischaemic lesions or the bubbles themselves. There may also be an accumulation of nitrogen bubbles in marrow fat.

Normal MRI of the cord does not rule out the diagnosis ³. If there are MRI findings, these tend to normalise after a few weeks.

Treatment

• hyperbaric oxygen therapy