Differentials
Gas toxicity (decompression illness)
SIGNS / SYMPTOMS
Contamination of breathing gas is rare, but carbon monoxide poisoning has occurred, causing symptoms such as headache, delirium, and loss of consciousness.[29] Symptoms may be present in other divers who have breathed gas from the same source.
INVESTIGATIONS
Analysis of the breathing gas and measurement of carboxyhaemoglobin levels will confirm exposure.
Hypercapnia
SIGNS / SYMPTOMS
Strenuous exertion or 'skip breathing' (intentional hypoventilation while underwater) can cause severe headache during or after a dive. Decompression illness will normally exhibit other features in addition to headache.
INVESTIGATIONS
Diagnosis is clinical.
Hyperventilation
SIGNS / SYMPTOMS
May cause transient peripheral paraesthesia in the hands, especially if the diver is anxious or dyspnoeic. Accompanying subjective dizziness or perceptual disturbances may complicate diagnosis, but the symptoms subside once the diver is calm, or are relieved by re-breathing into an airtight container.
INVESTIGATIONS
Diagnosis is clinical.
Non-fatal drowning
SIGNS / SYMPTOMS
An obvious history of water aspiration favours non-fatal drowning, whereas in decompression illness multi-system symptoms are often present. However, cardiopulmonary manifestations of decompression illness may resemble those of non-fatal drowning (dyspnoea, cough, chest pain, pulmonary oedema). The two diagnoses may co-exist, and if in doubt, recompression is advised.
INVESTIGATIONS
Chest x-ray may show signs of water aspiration.
Pulmonary oedema
SIGNS / SYMPTOMS
Immersion at depth increases cardiac afterload and may therefore exacerbate cardiac failure.[30]
Immersion pulmonary oedema can also be seen, and is often associated with heavy exertion while swimming.
INVESTIGATIONS
Chest x-ray may show signs of acute pulmonary oedema. Peripheral edema may also be present.
Congestive heart failure
SIGNS / SYMPTOMS
Immersion in water increases cardiac afterload and may therefore cause cardiac failure.[30]
The symptoms become worse during ascent because available oxygen diminishes. Can be difficult to distinguish clinically from pulmonary barotrauma in the acute setting.
INVESTIGATIONS
Chest x-ray may show signs of acute pulmonary oedema.
Envenomation or toxin ingestion
SIGNS / SYMPTOMS
Suggested by a history of fish or shellfish ingestion, or by a bite, sting, or unusual mark on examination. Marine animal envenomation or ingestion of seafood toxins can produce a wide range of local and systemic symptoms consistent with decompression illness.
INVESTIGATIONS
Diagnosis is clinical.
Migraine
SIGNS / SYMPTOMS
Diving can trigger an attack and symptoms such as headache, visual disturbance, and hemiparesis can be seen in both migraines and DCS/AGE. Divers with a history of migraines whose symptoms conform to their stereotype can be observed initially, but atypical features or deterioration should prompt recompression.
INVESTIGATIONS
Diagnosis is clinical.
Stroke
SIGNS / SYMPTOMS
May present similarly to arterial gas embolism (AGE) or cerebral decompression sickness. Symptom onset within a few minutes of diving is more likely to be due to AGE.
INVESTIGATIONS
CT of the head demonstrates ischaemia or haemorrhage. A negative head CT does not exclude stroke.
Minor head injury
SIGNS / SYMPTOMS
May present similarly to cerebral decompression illness. There may be a history of head trauma or evidence on physical examination.
INVESTIGATIONS
Diagnosis is primarily clinical. CT of the head may demonstrate injury.
Acute coronary syndrome
SIGNS / SYMPTOMS
Chest pain can be seen in the setting of pulmonary barotrauma, DCS, or acute coronary syndrome. Dyspnoea secondary to ACS may be relieved by oxygen, and can be confused with cardiopulmonary decompression illness or pulmonary barotrauma.
INVESTIGATIONS
ECG may show typical ischaemic changes (e.g., ST elevation).
Troponin will be elevated in the setting of myocardial damage due to ischaemia.
Coronary angiography may show abnormal blood flow.
Serum creatine kinase may be elevated, but it can also be elevated in divers with AGE.[31]
Seizure
SIGNS / SYMPTOMS
A seizure due to epilepsy, an undiagnosed space-occupying lesion, or hypoglycaemia in a diabetic diver may be difficult to differentiate clinically from decompression illness. Seizure occurring at depth is unlikely to be secondary to arterial gas embolism or decompression sickness.
INVESTIGATIONS
EEG may show epileptiform activity.
MRI may demonstrate a space-occupying lesion.
Blood glucose level may be low.
Multiple sclerosis
SIGNS / SYMPTOMS
There may be similarities in symptoms of exacerbation of multiple sclerosis and neurological manifestations of decompression illness.
INVESTIGATIONS
MRI may show patches of demyelination.
Advanced neurological imaging should not delay treatment of an injured diver.
Guillain-Barre syndrome
SIGNS / SYMPTOMS
There may be similarities in symptoms of Guillain-Barre syndrome and neurological manifestations of decompression illness.
INVESTIGATIONS
Cerebrospinal fluid protein may be elevated. EMG and nerve conduction studies may show conduction slowing.
Testing should not delay treatment of an injured diver.
Acute transverse myelitis
SIGNS / SYMPTOMS
There may be similarities in symptoms of acute transverse myelitis and neurological manifestations of decompression illness.
INVESTIGATIONS
MRI of the spinal cord shows intrinsic lesions, confirming myelopathy. Cerebrospinal fluid may show pleocytosis, elevated protein, abnormal immunoglobulin production, and oligoclonal bands.
Testing should not delay treatment of an injured diver.
Sprains and strains, tenosynovitis
SIGNS / SYMPTOMS
History and examination may point to a traumatic cause for musculoskeletal pains, which are common in divers. Migratory or diffuse symptoms that are not attributable to other causes, should prompt consideration of recompression.
INVESTIGATIONS
Diagnosis is clinical.
Infection
SIGNS / SYMPTOMS
Non-specific malaise and generalised myalgia may be mistaken for the constitutional symptoms of decompression illness. Usually, clear features of infection will be present, such as fever, with supportive signs on examination.
INVESTIGATIONS
Diagnosis is clinical. WBC may be elevated.
Drugs
SIGNS / SYMPTOMS
The effects of analgesic or sedative medication overuse, may mimic subjective symptoms of decompression illness.[32] Temporal relation of symptoms to drug ingestion may be diagnostic.
Acute intoxication or hangover may cause neurological or behavioural changes, headache, nausea, and visual disturbances. A history of ingestion together with the timing of symptoms onset can aid in diagnosis.
INVESTIGATIONS
Diagnosis is clinical. Blood or urine testing may be positive for illicit substances.
Psychological problems, acute psychosis
SIGNS / SYMPTOMS
Inexperienced divers or those of a nervous disposition may focus on subjective symptoms to such an extent that exclusion of decompression illness may be impossible without recompression.
Acute psychosis with thought disorder, delusions, or hallucinations may mimic nitrogen narcosis. Rapid reversibility of the symptoms with ascent generally confirms the diagnosis of nitrogen narcosis.
INVESTIGATIONS
Diagnosis is clinical.
Pulmonary embolism
SIGNS / SYMPTOMS
May present with chest pain and dyspnoea. Difficult to distinguish clinically from barotraumas in the field.
INVESTIGATIONS
D-dimer may be positive. ECG changes may include tachycardia, right axis deviation, right bundle branch block, or the classic S wave in lead I and Q wave with T wave inversion in lead III. Computed tomographic pulmonary angiography (CTPA) confirms diagnosis by direct visualisation of thrombus in a pulmonary artery.
Acute exacerbation of asthma
SIGNS / SYMPTOMS
A past medical history of asthma in a diver needs careful assessment. Dry compressed gas, exercise, saltwater aspiration, and anxiety are all potential triggers for an asthma exacerbation while diving. Wheeze and diurnal variation of symptoms are rare in pulmonary barotrauma.
However, air trapping in asthmatics may increase risk for pulmonary barotrauma of ascent.
INVESTIGATIONS
Inhalation of a beta-2 agonist will improve symptoms.
Asthmatic patients should seek medical clearance from a diving medicine physician prior to diving due to increased risk of pulmonary barotrauma of ascent.
GORD
SIGNS / SYMPTOMS
Can occur during immersion, even with a normal lower oesophageal sphincter.[33] Symptoms of reflux and aspiration of gastric contents may be similar to those of pulmonary barotrauma, although a prior history of GORD may be present.
INVESTIGATIONS
Diagnosis is clinical.
Costochondritis
SIGNS / SYMPTOMS
Inflammation of the costochondral or costosternal joints may cause pleuritic chest pain. There is localised tenderness on palpation, and lung fields are clear on auscultation.
INVESTIGATIONS
Diagnosis is clinical.
Rib fracture
SIGNS / SYMPTOMS
A fractured rib may cause pleuritic-type chest pain. There may be a history of chest trauma. There is localised tenderness on palpation, and lung fields are clear on auscultation.
INVESTIGATIONS
Chest x-ray will reveal a fracture.
Otitis externa
SIGNS / SYMPTOMS
'Swimmer's ear' may cause itching, pain, ear drainage, or an inflamed pinna. Pushing the tragus classically causes pain. Otoscopy may show a swollen, erythematous external auditory canal.
INVESTIGATIONS
Diagnosis is clinical.
Otitis media
SIGNS / SYMPTOMS
Common in divers, and symptoms may mimic those of middle-ear barotrauma. Otoscopy may show a ulging erythematous tympanic membrane.
INVESTIGATIONS
Diagnosis is clinical.
Mastoiditis
SIGNS / SYMPTOMS
Untreated otitis media may occasionally progress to mastoiditis, with swelling and tenderness over the mastoid process.
INVESTIGATIONS
Diagnosis is clinical.
Alternobaric vertigo
SIGNS / SYMPTOMS
Asymmetrical middle-ear pressures on ascent may lead to unequal vestibular end-organ stimulation. This can be distinguished from ear barotrauma by its transient nature and the absence of otoscopic abnormalities.
INVESTIGATIONS
Diagnosis is clinical.
Labyrinthitis
SIGNS / SYMPTOMS
A history of recent upper respiratory tract infection may suggest labyrinthitis. Otherwise difficult to differentiate from ear barotrauma.
INVESTIGATIONS
Diagnosis is clinical.
Meniere's disease
SIGNS / SYMPTOMS
May present in a similar fashion to ear barotrauma or inner ear DCS. The attacks of vertigo tend to be unpredictable, severe, and incapacitating. Many patients have a family history. May be associated with hearing loss and tinnitus.
INVESTIGATIONS
Diagnosis is clinical.
Sinusitis
SIGNS / SYMPTOMS
A thick, purulent nasal discharge and fever may help to distinguish sinus infection from sinus barotrauma.
INVESTIGATIONS
Elevated WBC.
Dental infection
SIGNS / SYMPTOMS
Pain felt in the teeth may be due to local infection, referred pain from ipsilateral maxillary sinus barotrauma, or barodontalgia (caused by pressure changes in or around the teeth themselves).
INVESTIGATIONS
Elevated WBC in infection.
Epistaxis
SIGNS / SYMPTOMS
Vigorous equalising manoeuvres may cause epistaxis through localised shearing of nasal blood vessels, with the appearance of blood in the diving mask. May also be seen in the setting of sinus barotrauma.
INVESTIGATIONS
Diagnosis is clinical.
Hypoglycaemia
SIGNS / SYMPTOMS
May be difficult to differentiate clinically from nitrogen narcosis while at depth.
INVESTIGATIONS
Low blood glucose level.
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