By Herbert B. Newton, M.D.
Diving injuries involving the nervous system, including decompression sickness (DCS), arterial gas embolism (AGE) and ear barotrauma (EBT), are blessedly rare, but when they do happen, these conditions require prompt diagnosis and treatment to prevent serious and lasting injury.
1.Cerebral DCS vs. 3. Spinal DCS
Common symptoms: Distinguishing between spinal and cerebral manifestation of DCS is of academic interest only, and the treatment – emergency oxygen and hyperbaric therapy – is the same. Cerebral symptoms are present in 30 to 40 percent of neurological DCS cases, while spinal cord symptoms are found in 50 to 60 percent of neurological DCS cases
How to tell the difference: Spinal DCS is caused by spinal cord damage, most often in the thoracic segment. Patients complain of paresthesias (i.e., pins and needles) and sensory loss in the trunk and extremities, a tingling or constricting sensation around the chest or abdomen, ascending leg weakness that can range from mild to severe, lower back or pelvic pain and loss of bowel and/or bladder control. The neurological examination will often reveal weakness or paralysis of both legs and a partial or complete loss of sensation.
Cerebral DCS can occur alone or in combination with spinal DCS and manifests as confusion, weakness, headache, gait disturbance, fatigue, diplopia (i.e., double vision) or visual loss. The neurological examination may show hemiparesis (i.e., weakness on right or left side), dysphasia (i.e., disturbance of speech and language), loss of balance and difficulty with gait, partial loss of vision in both eyes and other focal signs. Behavioural and cognitive aspects of cerebral DCS may be persistent or slow to improve.
Special cases: In the case of a mild spinal DCS injury, a diver may initially complain of lower back pain and bilateral leg numbness and yet still have normal strength and sensation.
2. Ear Barotrauma vs. Inner-Ear DCS System
Both ear barotraumas and inner-ear DCS can cause vertigo (a severe spinning sensation), hearing loss, tinnitus (ringing in the ear), nausea and vomiting.
How to tell the difference:
Ear barotrauma symptoms occur abruptly during descent or in the course of an ascent. Inner-ear DCS symptoms usually occur within 30 to 60 minutes of surfacing and generally require significant depth-time exposure.
Special cases: Middle-ear barotrauma is usually associated with the acute onset of ear pain. It may involve bleeding, rupture of the eardrum and fullness of the ear. Inner-ear barotrauma can develop secondarily in individuals with middle-ear barotrauma, causing rupture of the labyrinth and leakage of liquid from the inner ear.
In rare situations, the increase in middle-ear pressure during a normal ascent can cause reversible injury of the facial nerve and weakness of the facial muscles. Vertigo can also occur if the pressure is different on the vestibular organs of the ear (those in the middle cavity of the ear). That condition is alternobaric vertigo. Both conditions resolve after pressure equalisation.
AGE vs. DCS
Common symptoms: Arterial gas embolism, or “AGE”, can mimic DCS, and distinguishing between the two injuries may be impossible in some cases. In rare cases, both AGE and DCS can develop simultaneously. The two syndromes are often described and treated together using the more global term decompression illness (DCI).
How to tell the difference:
AGE symptoms occur within minutes after surfacing and can occur regardless of the depth or duration of the dive. Almost two-thirds of individuals with AGE have a reduced level of consciousness. Seizures, focal motor weakness, visual loss, vertigo and sensory changes are also frequently noted in AGE victims. DCS symptoms generally occur after deep or long dives, and symptoms may take up to 24 hours to present; however, in most DCS cases, symptoms were noticed within 12 hours of the diver surfacing.
Special cases: AGE may be associated with subcutaneous emphysema (air under the skin of the upper chest and/or neck) or pneumothorax (collapsed lung), but pulmonary symptoms are not always present.