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. 
The vertebral arteries arise from the subclavian arteries. They enter the skull through the foremen magnum and merge to form the basilar artery at the pontomedullary junction. The posterior inferior cerebellar artery (PICA) is derived from each vertebral artery. PICA supplies the medulla and the suboccipital surface in the part of the cerebellum. When there is decreased blood flow to these regions, patients typically present with signs and symptoms of posterior circulation stroke which are discussed later.
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 most prevalent 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%) of cases 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 most common mechanism of occlusion of the vertebral artery or PICA is atherothrombosis.
Atherosclerosis is the most common condition affecting the vertebrobasilar system, in which atheromatous plaques narrow and occlude large vessels. However, the pathology of small vessel disease is different as compared to that of large vessels which are affected by atherosclerosis. Small vessels are affected by a process called lipohyalinosis, which is closely associated with hypertension. Ischemic infarctions of these small vessels lead to small round infarctions called lacunae, which are scattered throughout the brainstem.
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 progress 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 a key to the diagnosis. A complete Wallenberg syndrome is not common, yet partial syndromes are satisfactory 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, wherein 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 marked 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 (DWI) 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 the 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 to rule out uncommon causes such as vertebral artery dissection.
An ECG is useful in excluding any underlying atrial fibrillation or unexpected acute coronary syndrome. Checking the serum electrolytes is essential. Patients with dysphagia or dysarthria need to be assessed by the speech pathologist before 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 outcomes. 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 is decided after the outcome of the primary prevention of each patient. This will again include a multimodality approach:
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.
Stroke syndromes, in general, can cause permanent disability and affect the normal functioning of the patient. The most common complications of posterior circulation strokes are aspiration pneumonia, deep vein thrombosis, pulmonary embolism, and myocardial infarction. Mechanical ventilation and the use of nasogastric tube further increase the risk of lung infections.
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 is the most typical sequelae. Sometimes hiccups 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. Preferably, a specialty trained neurologist and neurology specialty nurse should assist with the coordination of care of the patient, monitoring, and patient education, keeping other team members apprised of findings and issues. The pharmacist should evaluate for potential drug-drug interactions and assist with appropriate dosing as well as with patient education, coordinating with the clinical staff if any medication changes are necessary. An interprofessional approach will lead to improved outcomes. [Level 5]
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