Editing Decompression sickness (section)

== Diagnosis ==
Diagnosis of decompression sickness relies almost entirely on clinical presentation, as there are no laboratory tests that can incontrovertibly confirm or reject the diagnosis. Various blood tests have been proposed, but they are not specific for decompression sickness, they are of uncertain utility and are not in general use.<ref name="Freiberger et al 2005" />

Decompression sickness should be suspected if any of the symptoms associated with the condition occurs following a drop in pressure, in particular, within 24 hours of diving.{{r|ThalmannDAN}} In 1995, 95% of all cases reported to [[Divers Alert Network]] had shown symptoms within 24 hours.{{r|DAN1995annual}} This window can be extended to 36 hours for ascent to altitude and 48 hours for prolonged exposure to altitude following diving.{{r|Cronje 2014}} An alternative diagnosis should be suspected if severe symptoms begin more than six hours following decompression without an altitude exposure or if any symptom occurs more than 24 hours after surfacing.{{r|MoonSPUMS98}} The diagnosis is confirmed if the symptoms are relieved by recompression.{{r|MoonSPUMS98 | 45UHMS}} Although [[magnetic resonance imaging]] (MRI) or [[computed tomography]] (CT) can frequently identify bubbles in DCS, they are not as good at determining the diagnosis as a proper history of the event and description of the symptoms.{{sfn|Marx|p=1908}}

===Test of pressure===
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There is no [[Gold standard (test)#In medicine|gold standard]] for diagnosis, and DCI experts are rare. Most of the chambers open to treatment of recreational divers and reporting to Diver's Alert Network see fewer than 10 cases per year, making it difficult for the attending doctors to develop experience in diagnosis. A method used by commercial diving supervisors when considering whether to recompress as first aid when they have a chamber on site, is known as the ''test of pressure''. The diver is checked for contraindications to recompression, and if none are present, recompressed. If the symptoms resolve or reduce during recompression, it is considered likely that a treatment schedule will be effective. The test is not entirely reliable, and both false positives and false negatives are possible, however in the commercial diving environment it is often considered worth treating when there is doubt,<ref name="Freiberger et al 2005" /> and very early recompression has a history of very high success rates and reduced number of treatments needed for complete resolution and minimal sequelae.<ref name="Doolette and Mitchell 2018" /><ref name="Mitchell et al 2018" />

===Differential diagnosis===
{{See also|Inner ear decompression sickness#Diagnosis}}

Symptoms of DCS and arterial gas embolism can be virtually indistinguishable. The most reliable way to tell the difference is based on the dive profile followed, as the probability of DCS depends on duration of exposure and magnitude of pressure, whereas AGE depends entirely on the performance of the ascent. In many cases it is not possible to distinguish between the two, but as the treatment is the same in such cases it does not usually matter.{{r|Cronje 2014}}

Other conditions which may be confused include skin symptoms. ''[[Cutis marmorata]]'' due to DCS may be confused with [[Barotrauma#In divers|skin barotrauma]] due to [[Dry suit#Suit squeeze|dry suit squeeze]], for which no treatment is necessary. Dry suit squeeze produces lines of redness with possible bruising where the skin was pinched between folds of the suit, while the mottled effect of ''cutis marmorata'' is usually on skin where there is subcutaneous fat, and has no linear pattern.{{r|Cronje 2014}}

Transient episodes of severe neurological incapacitation with rapid spontaneous recovery shortly after a dive may be attributed to [[hypothermia]], but may actually be symptomatic of short term CNS involvement due to bubbles which form a short term gas embolism, then resolve, but which may leave residual problems which may cause relapses. These cases are thought to be under-diagnosed.{{r|Cronje 2014}}

[[Inner ear decompression sickness]] (IEDCS) can be confused with [[inner ear barotrauma]] (IEBt), [[alternobaric vertigo]], [[caloric vertigo]] and [[reverse squeeze]]. A history of difficulty in equalising the ears during the dive makes ear barotrauma more likely, but does not always eliminate the possibility of inner ear DCS, which is usually associated with deep, mixed gas dives with decompression stops.{{r|Cronje 2014}} Both conditions may exist concurrently, and it can be difficult to [[Inner ear decompression sickness#Differential diagnosis|distinguish whether a person has IEDCS, IEBt]], or both.

Numbness and tingling are associated with spinal DCS, but can also be caused by pressure on nerves (compression [[neurapraxia]]). In DCS the numbness or tingling is generally confined to one or a series of [[Dermatome (anatomy)|dermatomes]], while pressure on a nerve tends to produce characteristic areas of numbness associated with the specific nerve on only one side of the body distal to the pressure point.{{r|Cronje 2014}} A loss of strength or function is likely to be a medical emergency. A loss of feeling that lasts more than a minute or two indicates a need for immediate medical attention. It is only partial sensory changes, or [[paraesthesia]]s, where this distinction between trivial and more serious injuries applies.<ref name="Cronje 2009" />

Large areas of numbness with associated weakness or paralysis, especially if a whole limb is affected, are indicative of probable brain involvement and require urgent medical attention. Paraesthesias or weakness involving a dermatome indicate probable spinal cord or spinal nerve root involvement. Although it is possible that this may have other causes, such as an injured intervertebral disk, these symptoms indicate an urgent need for medical assessment. In combination with weakness, paralysis or loss of bowel or bladder control, they indicate a medical emergency.<ref name="Cronje 2009" />