Type II decompression sickness in naval hypobaric chambers: A case of mistaken identity?

Historically, U.S. Navy clinicians have used the U.S. Navy Dive Manual for guidance in the diagnosis and treatment of injuries incurred during hyper- or hypobaric operations. Based on this manual, paresthesias are considered to be central nervous system manifestations and thus are classified as Type II (severe) decompression sickness (DCS). Yet given the highly successful response to treatment of peripheral nervous system manifestations of DCS in the literature, both the diving and aviation communities have questioned its classification as "severe" DCS. This record review was undertaken to examine U.S. Naval severe cases of altitude DCS with the goal of identifying dissimilarities between hypobaric facilities in classification and incidence.

Hypobaric exposures and cases were reviewed from quarterly training reports maintained at the Naval Operational Medicine Institute, Pensacola, FL, between January 1993 and April 2004. Cases were analyzed for age, gender, flight profile, symptom complex, type of DCS, and treatment provided.

There were 50,355 hypobaric exposures resulting in 97 cases of altitude DCS. Of the 97 cases of diagnosed DCS, 58 were classified as Type II, while 39 were Type I. Of the 58 cases of Type II DCS, 29 were diagnosed as Type II by the sole finding of non-dermatomal paresthesias.

Type II DCS, a designation traditionally reserved for severe DCS, is frequently diagnosed by the sole finding of non-dermatomal paresthesias in Naval hypobaric training. A review and revision of the U.S. Naval Aviation classification system for altitude DCS should be undertaken with emphasis on severity not symptomatology.