By Charles A. Pilcher MD FACEP
February, 2016
In the November, 2015, issue of Medical Malpractice Bulletin, “Perspective” covered the issue of missed aortic dissections. Missed dissections result in nearly 200 times more lawsuits than missed MI’s – on the basis of frequency of presentation to the ED.
This month I cover posterior circulation strokes, another common missed diagnosis often treated as a simple inner ear disorder.
As described in November, chest pain has a wide range of causes, aortic dissection being one of them. Likewise, vertigo, the most common symptom of posterior circulation stroke, has many causes. Just as chest pain can be benign (think pleurisy), vertigo is also usually benign. But whereas the most common “rule out” for chest pain is an acute MI, definitely serious, the most common “rule out” for vertigo is an inner ear problem, definitely not serious.
The point here is that a diagnostic error can be made in different ways. In either case a narrow focus and “anchoring bias” is the most common cause of diagnostic error. Confidently ruling out an MI (serious) in a chest pain patient while missing the aortic dissection (equally serious) is just as dangerous as confidently ruling in labyrinthitis or benign positional vertigo (not serious) while missing the posterior circulation stroke (serious). In both cases a broad differential diagnosis and critical thinking is necessary to avoid error.
While anterior circulation strokes involve branches of the internal carotid arteries such as the middle cerebral artery, posterior circulation strokes involve branches of the vertebral-basilar system such as the vertebral artery or cerebellar artery.
Presentation:
The symptoms of a posterior circulation stroke typically include the following:
- younger than most stroke patients,
- older than most patients with simple vertigo,
- sudden onset of dizziness,
- nausea and vomiting,
- an unstable gait,
- nystagmus,
- headache and
- occasionally neck pain.
The onset is generally more sudden than with other causes of dizziness; there is rarely a prodrome of any significant duration. The symptoms may wax and wane somewhat after onset, but they are persistent.
Anterior circulation strokes are typically characterized by motor and speech problems such as unilateral weakness, speech difficulty and problems with the cranial nerves (inability to smile, asymmetry of movement of the eyes or lips, etc.). Posterior circulation strokes involve the cerebellum and temporal lobes of the brain where coordination and proprioception (position in space) are controlled. Thus, since balance is part of one’s “position in space,” when that part of the brain malfunctions, one has the same feeling as being on a moving boat, i.e., dizziness and/or seasickness or nausea.
Causes:
Common causes of posterior circulation stroke include vertebral artery dissection due to neck trauma, vertebral artery thrombosis or embolism, and posterior circulation hemorrhage. Since the vertebral artery passes through the cervical vertebrae themselves, neck injury during chiropractic manipulation is also associated with these strokes.
Because these are all much less common than simple labyrinthitis or benign vertigo, they are much less likely to be top-of-mind for the examining physician.
But they must be, or they will be missed.
Diagnosis:
As with aortic dissections, the diagnosis of a posterior circulation stroke is not that difficult to make. Both diagnoses are most often missed because of failure to consider the possibility. Two common biases play a prominent role:
- Anchoring bias, or locking on to a diagnosis too early and failing to adjust to new information, and
- Knowledge bias, the tendency to choose the option one knows best rather than the best option.
When that happens, appropriate tests are not done resulting in diagnostic error.
Testing:
If a posterior circulation stroke is suspected, a CT angiogram or MR angiogram is the appropriate study.
Treatment:
A major difference between aortic dissections and posterior circulation strokes is that surgical treatment for the former is available when indicated. There is no strong consensus on appropriate treatment of the latter. Options studied include stenting, “clot-busting” drugs like tPA, heparin, aspirin alone, simple observation or more complicated mechanical clot removal. All have their proponents, but consensus is absent.
Legal Implications:
When multiple treatment options exist, the lack of consensus raises issues of causation. Even if a physician has indeed made the correct diagnosis and admitted the patient to the hospital, questions remain about the correct treatment and how much, if any, difference that treatment would make?
In every litigated case, an expert can be found who favors every available approach, including watchful waiting. Whether a defense or plaintiff attorney wishes to entrust the outcome of such cases to a jury of lay persons weighing the opinions of dueling experts is a significant challenge.
That said, no physician looks good when a posterior circulation stroke is missed and death or major disability results.
References:
- Delay in diagnosis of basilar artery stroke. Burns JD, et al. Neurocrit Care. 2015.
- Outcomes among patients discharged from the emergency department with a diagnosis of peripheral vertigo. Atzema et al, Annals of Neurology, January 2016
- Missed stroke in acute vertigo and dizziness: It is time for action, not debate. Newman-Toker D. Annals of Neurology, January 2016