Man in a Barrel Syndrome

Etiology

Man in a barrel syndrome can result from bilateral watershed strokes due to systemic hypotension, such as seen in cardiac arrest.

• The internal carotid artery supplies blood flow to the anterior two-thirds of the brain via the anterior cerebral artery (ACA) and the middle cerebral artery (MCA). The most distal branches of the ACA and MCA supply brain tissue, including upper extremity motor fibers. In the setting of inadequate blood flow to both sides, the brain, these most distal branches, or watershed zones, do not receive an adequate amount of oxygenated blood, resulting in the death of these cells. Based on the neuroanatomy of these anterior circulation watershed zones, damage to these areas can result in bilateral upper extremity weakness.[2]

• Any lesion affecting the bilateral upper extremity motor fibers can result in similar clinical findings of bilateral upper extremity weakness - including hemorrhage, inflammatory lesions, traumatic injury, or neoplastic or metastatic disease.[3]

• Acute ischemia in the brainstem pyramidal decussation or cervical spinal cord, compressive or intrinsic cervical spinal cord lesions affecting upper extremity motor fibers while sparing lower extremity motor fibers, and peripheral neuropathic injury involving the bilateral nerve roots, brachial plexus, peripheral nerves, or neuromuscular junction can all result in MIBS.[4][5]

Epidemiology

Man in a barrel syndrome is a rare syndrome, and the exact incidence is unknown. MIBS affects men and women equally. Cerebral hypoperfusion causing bilateral watershed strokes is a common cause of MIBS.[6] Watershed strokes make up an estimated 10% of all ischemic strokes.[7]

Pathophysiology

Man in a barrel syndrome results from damage to the bilateral upper extremity motor fibers, sparing the bilateral lower extremity motor fibers. Bilateral symmetric damage isolated to the upper extremity motor fibers in the motor cortex, corona radiata, internal capsule, basal ganglia, brainstem, anterior spinal cord, cervical nerve roots, brachial plexus, peripheral nerves, or neuromuscular junction can result in MIBS. Damage to the anterior horn cells, such as in HTLV-1 or amyotrophic lateralizing sclerosis, can also present with bilateral upper extremity weakness.[8][9]

History and Physical

Evaluation with a detailed history and neurologic examination in which bilateral arm strength is impaired and bilateral cervical, facial, and leg strength is preserved are the first steps in diagnosing man in a barrel syndrome.

Neurologic examination in a patient with MIBS is significant for weakness in the bilateral upper extremities and preserved strength in the bilateral neck and lower extremities.

• Depending on the location of the neurologic injury, the mental status may be normal to severely impaired.
• In patients with a central nervous system injury such as stroke or a cervical spine lesion causing MIBS, reflexes are commonly brisk, whereas, in a peripheral nervous system dysfunction causing MIBS such as multifocal motor neuropathy, myasthenia gravis, or bilateral brachial plexus injuries, reflexes are diminished or absent.[10]

Once the clinical diagnosis of MIBS is made based on the neurologic exam, the next step is to localize the causative lesion(s).

• History may suggest the location of the injury; for example, MIBS following a cardiac arrest with prolonged time without a pulse suggests bilateral watershed strokes, whereas a recent neck injury suggests a cervical spine lesion or bilateral upper extremity injury suggests bilateral brachial plexus injury.
• Recent surgery with the traction of the arms can suggest a bilateral brachial plexopathy.[11][12][1]

Evaluation

Once the clinical diagnosis of MIBS is made, the next step is to localize the lesion(s), causing bilateral upper extremity weakness.

• Brain imaging with magnetic resonance imaging (MRI) or computed tomography (CT) can identify intracranial ischemic, hemorrhagic, metastatic, or inflammatory lesions. Cervical spine imaging with CT can identify and compressive cervical spine lesion, and MRI of the cervical spine can localize any extrinsic compressive or intrinsic lesion in the cervical spine.

• If the brain and cervical spine imaging do not reveal a cause of MIBS, the brachial plexuses should be evaluated, MRI can identify injury to the brachial plexus, and electromyography (EMG) / nerve conduction studies can identify the location of the nerve root, brachial plexus or peripheral nerve dysfunction.

• Watershed stroke is the most common cause of MIBS; for patients with watershed stroke, imaging of the cervicocephalic arterial vasculature should be performed to evaluate for any flow-limiting stenoses. If significant flow-limiting stenoses are found in the internal carotid arteries, revascularization with carotid endarterectomy or stent placement may be beneficial to reduce the risk of subsequent stroke.[13]

Treatment / Management

Treatment for man in a barrel syndrome varies dependent upon the location and type of neurologic injury.

• For patients with watershed stroke, treatment includes maintaining adequate blood pressure to prevent extension of stroke, evaluation for any arterial stenosis which may have predisposed to hypoperfusion, initiation of antithrombotic medication, and correction of the underlying abnormality causing hypotension.

• For compressive cervical spine lesions, emergent surgical decompression should be considered. Intrinsic cervical spinal inflammatory conditions can be treated with steroids. Physical therapy and occupational therapy treatment are important to help improve functional recovery in man in a barrel syndrome.

Differential Diagnosis

The differential diagnosis for man in a barrel syndrome includes the following lesions along the neuroaxis:

1. Bilateral cerebral upper extremity motor fibers (watershed ischemic stroke, hemorrhagic, traumatic injury, inflammatory, metastatic disease) 
2. Cervical spine (external compressive lesion, ischemia, inflammatory or infectious process) 
3. Bilateral brachial plexus (mechanical injury, inflammatory)
4. Peripheral neuropathic process (toxic or metabolic neuropathy, inflammatory, auto-immune such as multifocal motor neuropathy or myasthenia gravis)

Prognosis

The prognosis for man in a barrel syndrome depends on the type and location of the lesion(s). The prognosis for recovery from bilateral watershed strokes is variable depending on the extent of ischemic damage. In comatose patients with MIBS following extensive watershed strokes, survival is less than 10%.[6] Bilateral intracerebral hemorrhage tends to have a poor prognosis but depends on the extent of tissue damage. Recovery from cervical spine compressive lesions depends on how quickly the lesion is identified and surgically decompressed. MIBS due to myasthenia gravis can be fully reversible with treatment of myasthenia.[14]

Complications

Complications from bilateral intracerebral injury can include cognitive deficits, sensory loss, language dysfunction, weakness, and spasticity. Cervical spinal cord injury complications include weakness, sensory loss, spasticity and bowel, and bladder dysfunction. Bilateral brachial plexus injury complications include motor and sensory deficits in the bilateral upper extremities.