Mild Decompression Sickness: Clinical Manifestations

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).