Version August 2025
| Diving condition and key features | Differential diagnosis | Distinguishing features of the differential diagnosis |
| Inner ear decompression sickness (DCS): Cochlear symptoms are less common (33%) than vestibular symptoms (92%)[1]; symptoms begin during ascent or early after surfacing (within 60 minutes in 85% of cases); vertigo is typically sustained. | Inner ear barotrauma | Often associated with ear pain during descent; symptoms begin before surfacing in >50% of cases; cochlear symptoms are more common in barotrauma (94%)[1] |
| Vestibular migraine | Previous episodes unrelated to diving; often followed by typical headache | |
| Alternobaric vertigo | Caused by differing pressures in the middle ear during ascent or descent; always transient (lasting <1 minute) | |
| Benign paroxysmal positional vertigo | Typically recurrent (previous episodes unrelated to diving) and transient (duration of <1 minute) | |
| Seasickness | Common self-misdiagnosis; does not cause true vertigo or hearing loss | |
| Stroke | Patients with atypical symptoms or symptoms that fail to improve with hyperbaric oxygen treatment warrant evaluation for stroke | |
| Spinal DCS: Symptoms usually evolve relatively rapidly (within 1 to 2 hours after surfacing). | Epidural hematoma or abscess | Anticoagulant therapy associated with risk of hematoma; abscess usually causes systemic symptoms of infection, probably present before diving |
| Transverse myelitis, Guillain-Barré syndrome, MS | Typically slow evolution (potentially over a period of days); with MS, there is often a history of previous events unrelated to diving | |
| Cardiopulmonary DCS: Onset within 30 minutes after surfacing; associated with provocative dives (eg, >25 m, rapid ascent, omitted decompression). | Immersion pulmonary edema | Symptom onset before ascent in many cases and may occur on dives that would not cause DCS |
| Near drowning | History of panic or water aspiration during dive or at surface after dive | |
| Myocardial infarction | History of angina or risk factors; symptoms may occur before ascent | |
| Musculoskeletal DCS: May be multifocal. | Musculoskeletal injury | Usually unifocal and associated with a history of trauma or an activity (eg, lifting or straining) likely to cause injury; may be stereotypic in the case of a recurrent injury |
| Constitutional DCS (fatigue, malaise, headache) | Viral or bacterial infection | Often associated with other symptoms such as coryza and fever |
| Carbon dioxide retention | Common cause of headache after diving, particularly dives involving hard work | |
| Cerebral DCS | Carbon monoxide toxicity | May cause confusion and unconsciousness, but often with onset before ascent |
| Mixed neurologic and constitutional DCS | Toxic seafood ingestion | Ciguatera, paralytic shellfish poisoning, puffer fish poisoning; may cause nausea and vomiting, perioral paresthesia, and progressive, relatively slow onset of weakness |
| Cutaneous DCS | Environmental exposure/toxin or animal bite/sting | Obtain careful history of any environmental exposure (eg, touching coral) or animal bite or sting (eg, jellyfish) Observe distribution of rash; if only on exposed areas (ie, not covered by wetsuit), may be environmental |
| Arterial gas embolism (AGE): Onset within seconds to minutes after surfacing; often follows a rapid or panicked ascent. | Stroke | Occurrence within minutes after surfacing from a dive is a possible but unlikely coincidence |
| Seizure | A history of seizures (epilepsy) may be present | |
| Aura before migraine | Previous events unrelated to diving; often followed by the typical headache | |
| Facial baroparesis | Caused by barotrauma to facial nerve in middle ear; history of middle ear pain during dive; upper and lower face involved, whereas AGE spares upper face | |
| Carotid or vertebral dissection | May be preceded by some form of neck trauma or strain; there may be anterior or posterior neck pain |
Adapted from: Mitchell SJ, Bennett MH, Moon RE. Decompression sickness and arterial gas embolism. N Engl J Med 2022; 386:1254. Copyright © 2022 Massachusetts Medical Society. Adapted with permission from Massachusetts Medical Society.
