Decompression Sickness: Differential Diagnosis

The attribution of symptoms following diving to DCS is contingent on the symptoms being qualitatively consistent with one or more of those described. In addition, an evaluation of the ‘provocation’ of the dive is useful but not definitive. Thus, a dive that breached no decompression limits without adequate decompression (see Chapter 12), involved rapid ascent or involved risk factors (see Chapter 12) would be considered more provocative than one that, for example, was well inside the no decompression limits with no untoward events. The timing of symptom onset (discussed previously in this chapter) is also contributory to diagnosis, with DCS becoming less likely with greater symptom latencies after diving. Unfortunately, there is no formula in which these various factors can be integrated to give a definitive answer on diagnosis. There is no substitute for knowledge and experience in this regard. Diagnostic uncertainty and the non-specific nature of many DCS symptoms will inevitably result in recompression of divers with consistent symptoms caused by another disorder from time to time. Other disorders that may mimic DCS are briefly considered here. Although the authors of this text emphasize the fact that a temporal relationship between diving and symptom onset is compelling evidence of a diving-related problem, DCS has many non-specific symptoms, and there are often several differential diagnoses that should be considered, especially in respect of some of the mild symptoms. Some of the more common or important differential diagnoses for DCS symptoms are outlined in this section.

Musculoskeletal pain is the most common single symptom of DCS, and it may also be caused by many other problems. Muscular and soft tissue injuries are common events in the diving environment, where there is heavy lifting and ample opportunity for minor trauma. This should be considered, especially where the diver has a non-migratory monoarthropathy with a history consistent with a non-DCS cause. Examination findings such as bruising may help, although cutis marmorata can look a little like bruising, so care is needed in interpreting skin change. There have been a few cases of myocardial ischaemia manifesting after diving with left shoulder and arm pain and being diagnosed as musculoskeletal DCS.

Fatigue is extremely common after diving, and the diagnosis of DCS would never be made on the presence of fatigue alone. Malaise can occur in many systemic illnesses, and in particular, viral illness can induce significant malaise. Such illnesses are common on diving trips, especially where participants have travelled long distances on airplanes and have been exposed to many other travellers. The presence of other viral illness symptoms such as fever and coryza, which are not usually seen in DCS, can help with accurate diagnosis.

Patchy paraesthesiae and rash can occur as a result of contact exposures with irritants such as marine stingers (see Chapter 32) and soaps used to clean wetsuits. Other allergies can cause rash, and some toxic ingestions that may occur on dive trips (e.g. ciguatera fish poisoning) (see Chapter 33) can cause marked widespread paraesthesiae, as well as myalgias and malaise.

Pulmonary symptoms, such as chest pain and cough, can occur in many settings. The main clue to DCS as a cause would be early onset (usually within minutes) after diving. Nevertheless, this does not rule out other causes of diving-induced pulmonary irritation such as pulmonary barotrauma (rare) (see Chapter 6), immersion pulmonary oedema (rare) (see Chapter 30), oxygen toxicity (very rare) (see Chapter 17), near drowning (see Chapter 22) or salt water aspiration syndrome (see Chapter 24). Pulmonary barotrauma could be suspected if there was a history of rapid or panicked ascent, if the dive was unprovocative for DCS or if there were clear signs of pulmonary barotrauma such as haemoptysis, pneumothorax or subcutaneous emphysema in the supraclavicular area. Immersion pulmonary oedema can be a difficult differential diagnosis, although the symptoms often first appear at depth and force termination of the dive. Symptoms that appear at depth are not DCS. In addition, although some descriptions of pulmonary DCS refer to the possibility of pulmonary oedema, these may represent misdiagnoses. Pulmonary oedema has not been a feature of definite pulmonary DCS seen by these authors. Oxygen toxicity symptoms would be expected only at the end of very long periods of oxygen exposure in technical diving (see Chapter 62). Near drowning would almost certainly be indicated by a clear history of some sort of distress event and inhalation of water. Salt water aspiration syndrome usually has a longer latency than pulmonary DCS. Moreover, in all these differential diagnoses, the symptoms would be limited to pulmonary involvement. The appearance of other DCS manifestations would point strongly to DCS as the diagnosis.

Spinal symptoms following diving are almost invariably the result of DCS. It is possible that degenerative spinal disease (e.g. ‘sciatica’) could manifest for the first time early after diving, but the symptoms would be unilateral and frequently preceded by a history of previous problems. The abdominal and back pain that may be a feature of spinal DCS can also occur in the Irukandji syndrome (see Chapter 32). Nevertheless, spinal symptoms arising early after diving should never be rationalized to an alternative diagnosis without an extremely good reason.

The diagnosis of inner ear DCS involves one of the most difficult and troublesome differential diagnoses in diving medicine – the separation between DCS and inner ear barotrauma (IEBT) (see Chapter 7). Both disorders may manifest with vestibular and/or cochlear symptoms early after diving, but the diagnoses have significantly different implications for subsequent management. DCS mandates recompression therapy, whereas recompression is relatively contraindicated in IEBT and these patients may warrant referral for round window surgery. A key point that frequently resolves the problem is that IEBT often manifests first during descent, and frequently in association with difficulty equalizing pressures in the middle ears. Manifestation before decompression rules out DCS, and a clear history of difficulty with ear ‘clearing’ increases suspicion of IEBT. A dive that is very non-provocative for DCS would also tip the diagnostic suspicion toward IEBT, whereas a more provocative dive would tip suspicion the other way, particularly if the dive involved a gas switch from a high-helium to a high-nitrogen mix, or if other manifestations of DCS emerged. Nevertheless, not infrequently there is ambiguity around the diagnosis, and difficult decisions about treatment have to be made.

Transient vertigo (usually lasting seconds) can also occur during ascent if there is a difference in the rates at which the middle ears vent expanding gas through the Eustachian tubes. This is known as ‘alternobaric vertigo’. This phenomenon is relatively common, transitory and self-limiting. Alternobaric vertigo should never be used as an explanation for persistent vestibular symptoms after a dive.

As previously discussed in relation to classification of the bubble-induced dysbaric disorders, there is often diagnostic ambiguity around the appearance cerebral symptoms after diving where the competing diagnoses are CAGE secondary to pulmonary barotrauma or cerebral DCS caused by the left-to-right shunting of VGE across a PFO or pulmonary shunts. The circumstances of the dive may provide definitive clues. For example, CAGE would be plausible and cerebral DCS highly implausible as an explanation for the rapid onset of focal cerebral symptoms after a panic ascent during training in a swimming pool. In addition, irrespective of the circumstances of the dive, it is likely that gross focal symptoms are more compatible with a CAGE event, whereas dysexecutive symptoms are more likely to be caused by DCS. However, in respect of cerebral DCS versus CAGE, the diagnosis is almost irrelevant because recompression according to the same regimen is now the prevalent response to either diagnosis (see Chapter 13).

Another possible cause of gross focal symptoms is a cerebrovascular event coincident with completion of a dive. Such events have occurred, and on occasion, divers suffering cerebrovascular accidents have been recompressed before the misdiagnosis has been discovered. This is unlikely to be harmful, although it will delay access to therapies such as thrombolysis or clot retrieval. Equally, because most cerebral symptoms appearing early after diving are caused by either DCS or CAGE, the prioritization of recompression as first-line therapy without detailed investigation to exclude cerebrovascular accident is appropriate for most cases.

Dysexecutive symptoms arising after diving may also be caused by a gas toxicity such as carbon monoxide exposure. The related symptoms are often initially noticed at depth, and this provides a clue that something other than DCS is responsible. There may also be a history of foul-tasting breathing gas or multiple divers affected if they breathed gas from a common source.

Fulminant Decompression Sickness: Clinical Manifestations

Fulminant DCS is a poorly defined entity, but the term is sometimes used to describe those cases in which, in addition to combinations of the foregoing symptoms, there is clear evidence of widespread systemic effects of bubbles such as haemoconcentration, shock and coagulopathy. This form of the disease is frequently fatal unless there is expert and comprehensive intervention. In this regard, it is notable that access to supportive therapy such as sedation, appropriate airway management, fluid resuscitation, and pharmacologic support of haemodynamics may be a more pressing priority than recompression per se. If patients with fulminant DCS are recompressed without appropriate supportive therapy in place, the outcome is likely to be poor.


CASE REPORT 11.1: A rebreather diver suffered an equipment malfunction after 9 minutes at 110-metre depth and made an uncontrolled ascent to the surface. He was sighted arriving at the surface and retrieved onto the boat, where he was found to be unconscious and apnoeic. He quickly resumed breathing and regained consciousness when cardiopulmonary resuscitation was initiated. A helicopter evacuation was extremely expeditious, and he arrived at a major tertiary hospital with a hyperbaric unit less than 1 hour after surfacing, having been treated with oxygen by a non-rebreather mask. He was complaining of dyspnoea and severe back pain. He had marked widespread cutis marmorata and quadriplegia. The pulse was 152, and peripheral pulses were unpalpable. The initial blood tests revealed marked haemoconcentration (haemoglobin, 254g/l), coagulopathy (activated partial thromboplastin time, 105; international normalized ratio, 2.0) and metabolic evidence of shock (pH, 7.24; lactate, 5; base excess, −12). He was diagnosed with fulminant DCS and catheterized, had large-bore intravenous access established, arterial and central venous lines placed and was aggressively fluid resuscitated and supported with vasopressors as the chamber was prepared for recompression. After sedation and intubation he was recompressed on a maximally extended US Navy Table 6. When sedation was withdrawn after 24 hours, he had recovered almost all motor function. After two further recompressions he, somewhat remarkably, made an essentially complete recovery.

Combined Presentations

The previously described manifestations can all appear in isolation, but combinations of symptoms are very common, particularly the constellation of symptoms described as constituting the mild DCS syndrome. Such combinations can be useful in helping to formulate the diagnosis. For example, whereas an isolated monoarthropathy after diving always raises suspicion of an alternative diagnosis such as a muscular strain, a monoarthropathy combined with patchy paraesthesiae and an erythematous rash would be a much more convincing basis for the diagnosis of DCS. Other common combinations include mild symptoms and any of the other forms of DCS, pulmonary DCS and spinal DCS, and cutis marmorata and spinal DCS.

Lymphatic Decompression Sickness: Clinical Manifestations

Lymphatic symptoms are among the more curious manifestations. Lymphatic DCS appears as subcutaneous swelling that is often surprisingly localized. It may lie over sites where there is musculoskeletal pain (which may be coincidental) or at other locations. The upper thorax and shoulder area appear selectively vulnerable. The disorder usually develops over a period of hours after diving and will eventually resolve whether the diver is recompressed or not. It is not usually painful, but it can create a conspicuously odd appearance (e.g. enlarging the breast area in a male patient). The natural history is to complete resolution, and there do not appear to be any long-term sequelae.

Cerebral Decompression Sickness: Clinical Manifestations

DCS can manifest with dysexecutive syndromes in which the diver complains of difficulties with concentration, memory, mood and other cognitive functions. These manifestations are frequently noticed ‘late’ when the diver returns home or to work. As described in Chapter 10, it seems most likely that such symptoms arise from exposure of the brain to VGE that have arterialized across a right-to-left shunt such as a PFO. It seems unlikely that these small VGE can cause the focal stroke-like manifestations typically associated with larger bubbles that may be introduced to the cerebral arterial circulation after pulmonary barotrauma. The latter type of presentation is described in Chapter 6. The natural history of cerebral DCS is poorly characterized, although the authors are aware of cases in which permanent cognitive sequelae have been reported.

Inner Ear Decompression Sickness: Clinical Manifestations

Inner ear DCS manifests with vestibular symptoms (vertigo, nausea, vomiting, ataxia) or cochlear symptoms (tinnitus, deafness) or both. Two distinct patterns of evolution are recognized. The first occurs during decompression from deep dives while the diver is still submerged, and it may be aggravated by a switch from a helium-based breathing gas to a nitrogen-based breathing gas. This is particularly dangerous because it can incapacitate the diver at a time when he or she still has hours of decompression to complete, thus forcing an early ascent with substantial missed decompression. The second occurs after arrival at the surface from more typical recreational air dives, although usually involving moderate depth exposure (greater than 25 metres). In this setting the onset is typically seen within the first 30 minutes of the dive. These different presentations probably have a different pathophysiological basis (see Chapter 10). Both may resolve spontaneously, but they are responsive to recompression and hyperbaric oxygen. Whether treated or untreated, it is certainly possible that long-term injury can follow inner ear DCS. In particular, permanent loss of hearing may occur. Although the vestibular apparatus may be permanently damaged, this does not usually result in long-term symptoms. There is a well-recognized ability for the brain to accommodate asymmetrical vestibular function that takes place over weeks to months and usually results in spontaneous resolution of vertigo and ataxia.

Spinal Decompression Sickness: Clinical Manifestations

All levels of the spinal cord may be involved, although a thoracolumbar distribution is most common. This disorder typically produces symptoms within the first 30 minutes after diving, and the first symptom is usually bilateral sensory change, which often ascends from distal to proximal, shortly followed by weakness producing ascending paraplegia. This is usually associated with a loss of bladder sensation and tone and a loss of anal tone. Cervical involvement may also produce sensory change and weakness in the upper limb. Examination findings are typically consistent with loss of upper motor neuron function under any circumstances, but in DCS there may be patchy involvement of different regions of the spinal cord, and detailed examination to delineate the location and extent of lesions is usually not necessary or helpful, especially at first presentation. Once the approximate extent of spinal involvement is understood, timely instigation of recompression treatment is the priority.

The natural history of spinal DCS is variable. In cases that progress to weakness, spontaneous recovery is possible, especially with surface oxygen administration. However, permanent sequelae are common even after treatment with recompression and hyperbaric oxygen. This makes spinal DCS the most feared and debilitating of the dysbaric diseases.

Cutaneous Decompression Sickness: Clinical Manifestations

The designation of superficial erythematous rash and itch as part of the mild constellation of DCS symptoms has already been discussed. The skin manifestation known as cutis marmorata sits outside the mild definition because of its frequent association with more serious manifestations. Cutis marmorata has a marbled, blotchy appearance in which areas of deep erythema and sometimes cyanotic change are interrupted and bounded by areas of pallor. The rash can evolve quite quickly and can even change appearance over a short period of observation. The rash can be itchy at first, but as it progresses it becomes less irritating or sometimes painful. Despite its often dramatic appearance, the rash almost invariably resolves with no obvious injury to the cutaneous tissues. The significance of cutis marmorata is its moderately frequent association with other more serious manifestations such as spinal DCS.

Pulmonary Decompression Sickness: Clinical Manifestations

Often referred to as cardiopulmonary DCS, this manifestation is rare and potentially fatal. The onset is usually early after diving and is more likely following a provocative profile (e.g. where decompression stops have been omitted for some reason). The diver may complain of cough and shortness of breath, which give rise to the colloquial name ‘the chokes’. There may also be retrosternal chest pain and a progression from confusion to loss of consciousness and collapse, the latter most likely reflecting rapidly progressive hypotension. Cardiac arrest and death may rapidly follow. Alternatively, the symptoms may spontaneously resolve; especially if oxygen breathing is quickly commenced because this almost certainly accelerates the resolution of VGE affecting the lungs. Because large numbers of VGE are required to produce pulmonary symptoms, it is not surprising that symptoms of involvement of other organs often accompany or follow pulmonary DCS. Thus, even if pulmonary symptoms begin to resolve, there should be a high index of suspicion for other manifestations.

Mild Decompression Sickness: Clinical Manifestations

A schema for classification of the clinical manifestations of DCS.

With the exception of the constellations of symptoms designated ‘mild’, ‘combined’, and ‘fulminant’, this section considers the clinical manifestations of DCS categorized by organ system. This corresponds to commonly used clinical terminology in which reference is often made to ‘spinal DCS’, ‘cerebral DCS’ and so forth in preference to the older type 1 and type II designations. A schema for classifying the clinical manifestations in this way is shown in Figure 11.1, which, for completeness, also puts DCS into the broader context of ‘decompression illness’ as described earlier.

A schema for classification of the clinical manifestations of DCS.
Figure 11.1 A schema for classification of the clinical manifestations of DCS.

Mild Decompression Sickness: It is logical first to discuss the constellation of symptoms that were defined as constituting ‘mild DCS’ by a consensus workshop hosted by Divers Alert Network (DAN) and the Undersea and Hyperbaric Medical Society (UHMS) in 20042. Presentations with one or more of the mild symptoms are the most common. Indeed, of 520 patients with cases treated at Auckland, New Zealand between 1995 and 2012, only 36 per cent had objective signs found on examination3. This is clinically significant because if the diver meets the agreed criteria for the mild designation, then the workshop consensus holds that he or she would not be disadvantaged in the long term if not recompressed. This, in turn, has important implications for decision making about evacuation and treatment for divers in remote locations; an issue that is discussed further later.

The symptoms in the mild category are as follows:

  1. Musculoskeletal pain.
  2. Subjective sensory changes in a non-dermatomal distribution.
  3. Constitutional symptoms such as fatigue and malaise.
  4. Itch and rash of the superficial erythematous type.

Musculoskeletal pain is the most frequent symptom in DCS (Figure 11.2). It is often described by patients as a ‘deep, boring ache’, and it may be severe. Various references characterize the typical location as ‘joint pain’, and indeed, it is commonly reported in hips, knees, shoulders and elbows. However, the localization is often poor, and extra-articular pain (e.g. the whole ‘upper arm’) is also well recorded. It is common for pain to exist in more than one location, and it may migrate. Affected divers often remark that unlike musculoskeletal pain they have suffered in other circumstances, there seems little they can do (e.g. adopting different positions and rubbing) to effect relief. In that regard, the use of a sphygmomanometer cuff as a diagnostic aid (inflating the cuff over the affected area allegedly compresses bubbles and provides relief) is not a valid strategy. It is notable that new back pain or abdominal pain following diving must never be automatically assumed to be musculoskeletal in origin. These symptoms may be indicative of spinal involvement that is yet to declare itself in a more obvious way.

Similarly, if a diver presents with bilateral and symmetrical shoulder or hip pain, a high index of suspicion must be maintained for spinal involvement, and other spinal manifestations (e.g. motor and sensory change) must be diligently excluded by competent examination.

Percentage of 520 DCS and CAGE cases complaining of various symptoms.
Figure 11.2 Percentage of 520 DCS and CAGE cases complaining of various symptoms. Note fatigue and lethargy appeared as separate entries in the database and so are shown separately here even though they likely represent the same phenomenon. SOB = shortness of breath, LOC = loss of consciousness.

Subjective sensory change is most commonly described as ‘patchy tingling’, and it is surprisingly common (see Figure 11.2). It may occur in multiple non-dermatomal distributions and may migrate. Sensory changes that lie in a dermatomal distribution are likely related to spinal involvement and do not meet the definition of mild.

Constitutional symptoms such as fatigue and a general sense of unwellness (malaise) are also common but very non-specific and difficult to interpret. Indeed, fatigue is an almost invariable consequence of a long day of diving. It would be most unusual to base a diagnosis of DCS solely on the presence of constitutional symptoms.

Itches and light erythematous or ‘scarlatiniform’ rashes, often with poorly defined boundaries, are less common than pain but still relatively frequent (Plate 3). They are usually proximal in distribution, with the trunk being the most common involved site. However, they can effectively occur anywhere. The cutis marmorata form of cutaneous DCS (see later) is not considered mild because it is often associated with neurological DCS, and that is why there is a separate ‘box’ for cutaneous DCS in Figure 11.1 even though most skin manifestations fit within the mild category.

The symptoms of the mild DCS syndrome are summarized in Figure 11.3. Another symptom that many physicians have retrospectively suggested should have been included in the mild category is headache. Headache is a very non-specific symptom and has many potential causes in diving. Although it is often reported by divers presenting with other symptoms of DCS, it would be extremely unusual to make the diagnosis of DCS based on a post-dive headache alone. At the present time headache sits outside the mild categorization laid down by the workshop2, but if a diver presented with mild symptoms (strictly as defined here) and a headache, then it would be reasonable to continue to designate the case as mild provided the other criteria outlined later are met.

Symptoms of DCS that were designated “mild” by the 2004 remote DCS workshop.
Figure 11.3 Symptoms of DCS that were designated “mild” by the 2004 remote DCS workshop.

In addition to fitting the qualitative symptom definitions described previously, the 2004 workshop also required compliance with a number of other conditions to designate a case as ‘mild’. First, the mild designation could not be applied while any of the symptoms were clearly worsening because this could herald the imminent appearance of new (and non-mild) symptoms. Second, the mild designation could not be applied unless the patient had undergone a competent neurological examination (which does not include ‘5-minute neuros’ by divers with no medical training). This stipulation recognized the potential for undetected objective neurological manifestations even when the obvious symptoms appeared mild. Third, in recognition of the potential for (rare) delayed deterioration, the mild designation should not be ‘signed off’ for 24 hours, and the patient should be periodically reviewed during this time.

The natural history of mild DCS symptoms (as defined earlier) is for spontaneous resolution even in the absence of therapy. There is little doubt that surface oxygen therapy will often accelerate recovery, and in respect of pain in particular, recompression and hyperbaric oxygen are likely to accelerate resolution markedly. Despite this potential for accelerated symptom resolution by recompression, the 2004 consensus workshop2 concluded that provided the presentation met the criteria for mild DCS, there was little or no evidence for any long-term disadvantage if the patient was not recompressed. It must be emphasized that the workshop was not advocating withholding of recompression for all patients with mild cases. Indeed, if recompression is readily available, then the best course of action is to treat the diver. However, the workshop did identify surface oxygen and other adjuvants (see Chapter 13) as acceptable alternatives to recompression in mild cases where recompression would be difficult or hazardous to access (e.g. in a very remote location).