Medial Medullary Syndrome

Etiology

Medial medullary syndrome is most commonly caused by atherothrombotic occlusion of the paramedian branches of the anterior spinal artery, the vertebral artery, or the basilar artery. Common risk factors are dyslipidemia, hypertension, diabetes, and smoking. Other risk factors are atrial fibrillation, atrial septal defect, patent foramen ovale, migraine, and Takayasu arteritis. Dissection of the vertebral artery can also cause medial medullary syndrome, especially among young patients.[2][3][4]

Epidemiology

Stroke is the world's second-largest cause of death and a major cause of disability. There are almost 800,000 patients in the United States who suffer from an acute stroke every year. Of these strokes, 83 percent are ischemic strokes. 20 to 25% of ischemic strokes occur due to vertebrobasilar artery occlusion (posterior circulation). A variety of neurological syndromes can occur in posterior circulation stroke, medial medullary syndrome is one of them and is a rare cause of ischemic stroke. Approximately 1% of cerebral infarction is due to medial medullary syndrome.[5][6]

Pathophysiology

Medial medullary syndrome is caused by a lesion in the medial part of the medulla, which is due to an infraction of vertebral arteries and/or paramedian branches of the anterior spinal artery. So, medial medullary structures, including the lateral corticospinal tract, medial lemniscus, and hypoglossal nerve, are commonly damaged in medial medullary syndrome.

The lateral corticospinal tract controls the voluntary movement of contralateral limbs of the body. The medial lemniscus receives sensory (vibration, fine touch, and proprioception) input from the contralateral nucleus cuneatus or nucleus gracilis and sends this signal to the sensory cortex of the brain.[7] Due to the involvement of the caudal medulla, hypoglossal nerve (twelfth cranial nerve) damage may occur. The hypoglossal nerve supplies the intrinsic and extrinsic muscles of the tongue except for palatoglossus.

The function of each muscle supplied by the hypoglossal nerve are described below:

• Genioglossus- Protrude the tongue forward from the root
• Hyoglossus- Retracts and depresses the tongue
• Styloglossus- Draws the tongue upward
• Intrinsic muscles (transversus, verticalis, superior/inferior longitudinalis)- By curving, shortening, narrowing the tongue, they change the shape of the tongue.[8][9]

History and Physical

Symptoms and Signs

Contralateral paralysis of the upper and lower limb of the body due to lateral corticospinal tract involvement is a common finding.[10][11] A contralateral decrease in proprioception, vibration, and/or fine touch sensation may occur if medial lemniscus involvement is present in medial medullary syndrome. Some patients report paresthesias or less commonly dysesthesias in the contralateral trunk and lower limb. There are no objective signs of position, touch, or vibration sense loss in many patients with sensory symptoms. In certain patients, a slight loss of position and vibration sense with proprioceptive dysfunction in the contralateral foot is observed.[12] 

Ipsilateral deviation of the tongue due to ipsilateral hypoglossal nerve damage (the lower motor type of lesion) can be seen. Although dysphagia is commonly seen in patients with lateral medullary syndrome, it is more common in the bilateral medial medullary infarct.[13] In a review of 28 cases of bilateral medial medullary infarct state, they found 11 cases of dysphagia or palatal palsy.[14]

Evaluation

For evaluation of the patients, it is important to take a relevant clinical history, perform a physical examination, and do appropriate diagnostic tests including:

Risk factors evaluation: Search for risk factors of stroke, including dyslipidemia, hypertension, diabetes, smoking, atrial fibrillation, atrial septal defect, migraine, and Takayasu arteritis.

Neurological examination: A complete neurological examination should be done as medial medullary syndrome is mostly a clinical diagnosis.

Imaging: For the diagnosis of medial medullary syndrome, both computerized tomography (CT) scan and magnetic resonance imaging (MRI) should be done. MRI can visualize the lesion more effectively than a CT scan. It is difficult to visualize posterior cranial fossa structures by CT scan, which may be obscured by the bony structures on CT scan. In diffusion-weighted (DWI) and T2-weighted film, there will be a hyperintense lesion in the medial medulla.[2][15]

For identifying the site of vascular occlusion, a magnetic resonance (MR) angiogram or CT angiogram can be done.

An ECG can be performed for excluding underlying atrial fibrillation.

Other baseline investigations, including serum glucose, serum electrolytes, fasting lipid panel, etc., should be performed as well.

Treatment / Management

Management of medial medullary syndrome is similar to any acute ischemic stroke. A rapid evaluation of the patient is necessary for proper management. Management in a stroke center will decrease the mortality and morbidity of these patients.

Prehospital Management

• Assess and manage ABCs, give supplemental oxygen to maintain O2 saturation >94%
• Initiate cardiac monitoring if possible
• Establish IV access per local protocol
• Measure blood glucose and treat it accordingly
• Keep the patient NPO
• Transport the patient to the nearest most appropriate stroke center

Intrahospital Management Steps

• Initiate intravenous (IV) recombinant tissue plasminogen activator (rtPA) for thrombolysis within 3 or 4.5 hours of ischemic stroke symptom onset, according to inclusion and exclusion criteria. The benefit of this therapy is dependent on time. So it should be started as soon as possible. After IV thrombolysis, patients should be monitored for 24 hours in the intensive care unit (ICU) or stroke bed/unit.
• Endovascular intervention: Endovascular treatment options include intra-arterial fibrinolysis, mechanical clot aspiration with the Penumbra system, and acute angioplasty and stenting. These newer techniques improve outcomes in different patients, but they are usually only indicated in patients with large vessel occlusion.[16]

General Therapy

• Using normal saline is a good option, but hypotonic saline should be avoided as it can cause cerebral edema.
• Impairment of cerebral autoregulation occurs in the infarcted area of the brain. If BP is more than 220/120 or patients receive intravenous thrombolysis, then administer medications to lower the blood pressure. The blood pressure should come down gradually.
• Try to keep the patient's blood sugar within normal limits.
• Treatment of concomitant medical disease is important.
• Swallowing assessment before the patient receives oral medications, begins eating or drinking.
• Suspected pneumonia patients should be treated with appropriate antibiotics.
• Subcutaneous administration of anticoagulants to prevent DVT is recommended for the treatment of immobilized patients.
• Avoid routine placement of indwelling bladder catheters as it is associated with an increased risk of catheter-associated UTIs.
• Early appropriate physical and occupational therapy should be started along with rehabilitation.

Potential Discharge Medications

• Oral anticoagulation if the source of thrombus is the heart (i.e., atrial fibrillation)
• Antiplatelets such as clopidogrel, aspirin, or dipyridamole/ASA combination for other sources of thrombus[17]
• Statins to treat dyslipidemia

Differential Diagnosis

• Advanced amyotrophic lateral sclerosis (ALS)
• Hemimedullary infraction
• Hypoglossal nerve injury
• Brown-Sequard syndrome
• Intracranial tumor
• Posterior cord syndrome (PCS)

Prognosis

As the brain is permanent tissue, any injury to the brain is not completely reversible. With the advancement of medical science, nowadays, early diagnosis and early initiation of treatment, and the use of rehabilitative services, medial medullary syndrome has a fair prognosis. If the patient presents with severe hemiparesis and hemi-sensory loss, then residual hemiparesis and sensory loss may remain for the lifetime. A review of 26 previously reported cases that had bilateral lesions and presented with lingual paresis, quadriplegia, and respiratory symptoms had a bad prognosis.[18]

Complications

The most common complications of medial medullary syndrome are deep vein thrombosis (DVT) and pulmonary embolism (PE). Patients may develop severe dysphagia, especially patients with bilateral medial medullary syndrome. Patients can develop aspiration pneumonia. If immediate management is not initiated, then the condition can be fatal. Pulmonary embolism can present with sudden onset dyspnea, which can lead to death. Patients with hemiplegia may develop bedsores. Bedsores can be further complicated by infections and may progress to septicemia and death.[14][19]