Wallenberg syndrome is also known as lateral medullary syndrome or the posterior inferior cerebellar artery syndrome. Wallenberg described the first case in 1895. This neurological disorder is associated with a variety of symptoms that occur as a result of damage to the lateral segment of the medulla posterior to the inferior olivary nucleus. It is the most typical posterior circulation ischemic stroke syndrome in clinical practice. 
Wallenberg syndrome is caused most commonly by atherothrombotic occlusion of the vertebral artery, followed most frequently by the posterior inferior cerebellar artery, and least often, the medullary arteries. Hypertension is the commonest risk factor followed by smoking and diabetes. Cerebral embolism is a less frequent cause of the infarction. The other important cause to remember is vertebral artery dissection which may have risk factors including neck manipulation or injury, Marfan syndrome, Ehlers Danlos syndrome, and fibromuscular dysplasia. Vertebral artery dissection is the commonest cause of Wallenberg syndrome in younger patients.
Wallenberg syndrome is the most prevalent posterior ischemic stroke syndrome. There are nearly 800,000 patients who suffer from an acute stroke each year in the United States. Of these, 83% are ischemic strokes. Twenty percent of the ischemic strokes occur in the posterior circulation. If clinicians assume that about half of these suffer from Wallenberg syndrome, it can be estimated that there are more than 60,000 new cases of Wallenberg syndrome each year in the United States. There is a predominance of men in their sixth decade. Large artery atherothrombotic causes account for about 75% of the cases followed by cardioembolism in 17% and vertebral dissection in 8%.
The primary pathology of Wallenberg syndrome is occlusion of the posterior inferior cerebellar artery (PICA) or one of its branches. The syndrome can also be due to occlusion of the vertebral artery, or the inferior, middle, or superior medullary vessels. Anatomically the infarcted area in Wallenberg syndrome is supplied by the posterior inferior cerebellar artery (PICA). It turns out occlusion of the PICA accounts for only a small number of cases. The majority (80%) are caused by occlusion of the vertebral artery which gives rise to the PICA and the anterior spinal artery before it joins with the opposite vertebral artery to form the basilar artery. The commonest mechanism of occlusion of the vertebral artery or PICA is atherothrombosis.
A typical patient with Wallenberg syndrome is an elderly patient with vascular risk factors. Like any acute stroke syndrome, the onset is acute. The most common symptoms of onset are dizziness with vertigo, loss of balance with gait instability, hoarseness of voice and difficulty swallowing. The symptoms often progressed over several hours to sometimes a couple of days. 
Usually, there is no weakness associated with this syndrome and so this condition is often misdiagnosed or missed. A careful neurological examination is key to the diagnosis. A complete Wallenberg syndrome is not common, yet partial syndromes are good enough for the diagnosis most of the time. The important points in clinical diagnosis are a combination of crossed hemiparesis or hemianesthesia to indicate a brainstem lesion and the involvement of structures in the posterolateral medulla to localize where in the brainstem.
Different combinations of the following deficits may all be found in Wallenberg syndrome:
On the side of lesion:
On the contralateral side:
It is clinically interesting to note that more rostral lesions tend to be more ventrally located. These patients present with more dysphagia and dysphonia due to the involvement of the nucleus ambiguus. More caudal lesions involve more dorsolateral structures. These patients present with vertigo, ataxia, nausea/vomiting, and Horner syndrome.
The clinical differential diagnoses include:
The diagnosis is usually made or suspected from a clinical exam and history of presentation. MRI with diffusion-weighted imaging is the best diagnostic test to confirm the infarct in the inferior cerebellar area or lateral medulla. Up to 30% of patients with nondisabling stroke do not have a lesion on DWI-MRI brain. These patients are DWI-negative stroke patients and secondary prevention should be started to prevent future strokes. 
A CT angiogram or MR angiogram is very helpful in identifying the site of vascular occlusion and rule out uncommon causes such as vertebral artery dissection.
An ECG is helpful in excluding any underlying atrial fibrillation or unexpected acute coronary syndrome.
Checking the serum electrolytes is important.
Patient with dysphagia or dysarthria needs to be assessed by the speech pathologist because any food or medicine can be given orally.
Similar to the management of any acute ischemic stroke, remember "TIME IS BRAIN." Rapid evaluation is essential to an orderly approach(algorithm) developed within each hospital or stroke center. Management in certified stroke centers has shown to improve overall patient outcome. Treatment aims at reducing the size of infarction and preventing any medical complication with the final target of improving patient outcome and prognosis. 
The management steps include:
Secondary stroke prevention will be decided soon. This will again include a multimodality approach:
This multimodal approach can reduce the risk of subsequent stroke by 80%.
Overall Wallenberg syndrome has a better functional outcome than most other stroke syndromes. Most patients can return to satisfactory activities of daily living. The commonest sequel is gait instability.
Hypertension is the commonest risk factor. Atherothrombosis of the vertebral artery is the most frequent underlying vascular cause. Vertebral artery dissection needs to be considered in younger patients especially with a history of trauma, neck manipulation, or underlying collagen disorders such as Marfan syndrome. Head thrust (head impulse) test in the emergency department can differentiate peripheral vertigo due to acute labyrinthitis from central cause due to Wallenberg syndrome. The outlook for patients with Wallenberg syndrome depends on the size of the infarct, but in general, most patients have a better outcome compared with other ischemic stroke syndromes with the exception of some lacunar syndromes. Gait instability or ataxia are the most typical sequelae. Sometime hiccup can be intractable.
Treatment of Wallenberg Syndrome requires a rapid response and coordinated team approach involving clinicians, nurses, and pharmacists to provide the patient with the best possible outcome. [Level V]
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