Relationship between the clinical features of neurological decompression illness and its causes

There is dispute as to whether paradoxical gas embolism is an important aet iological factor in neurological decompression illness, particularly when t he spinal cord is affected. We performed a blind case-controlled study to d etermine the relationship between manifestations of neurological decompress ion illness and causes in 100 consecutive divers with neurological decompre ssion illness and 123 unaffected historical control divers. The clinical ef fects of neurological decompression illness (including the sites of lesions and latency of onset) were correlated with the presence of right-to-left s hunts, lung disease and a provocative dive profile. The prevalence and size of shunts determined by contrast echocardiography were compared in affecte d divers and controls. Right-to-left shunts, particularly those which were large and present without a Valsalva manoeuvre, were significantly more com mon in divers who had neurological decompression illness than in controls ( P < 0.001). Shunts graded as large or medium in size were present in 52% of affected divers and 12.2% of controls (P < 0.001). Spinal decompression il lness occurred in 26 out of 52 divers with large or medium shunts and in 12 out of 48 without (P < 0.02). The distribution of latencies of symptoms di ffered markedly in the 52 divers with a large or medium shunt and in the 30 divers who had lung disease or a provocative dive profile. In most cases o f neurological decompression illness the cause can be determined by taking a history of the dive profile and latency of onset, and by performing inves tigations to detect a right-to-left shunt and lung disease. Using this info rmation it is possible to advise divers on the risk of returning to diving and on ways of reducing the risk if diving is resumed. Most cases of spinal decompression illness are associated with a right-to-left shunt.