Symptom Finder - Monoplegia
MONOPLEGIA
Monoplegia is the paralysis of one extremity. Following the nerve impulse from the cerebral cortex down through the spinal cord, nerve roots, brachial and lumbosacral plexus, peripheral nerve, myoneural junction, and muscles allows us to recall the most significant causes of monoplegia.
Cerebral cortex: Monoplegia may result from a parasagittal tumor or abscess and anterior cerebral artery embolism or thrombosis. Occasionally an occlusion of the middle cerebral artery or its branches may cause monoplegia of the upper extremity, but there are almost always neurologic signs in the lower extremities in these cases.
Spinal cord: Early space-occupying lesions of the spinal cord and amyotrophic lateral sclerosis may present with monoplegia. It is unlikely for multiple sclerosis or transverse myelitis to present this way.
Nerve roots: Poliomyelitis, progressive muscular atrophy, and herniated discs may present with monoplegia. Early cauda equina tumors may present with monoplegia as well.
Brachial plexus: This would bring to mind brachial plexus neuropathy, thoracic outlet syndrome, and Pancoast tumors.
Sciatic plexus: This would suggest sciatic neuritis or injury.
Peripheral nerve: Trauma or entrapment of the peripheral nerves may present as a monoplegia. Charcot–Marie tooth disease may begin in one extremity.
Myoneural junction: Myasthenia gravis or Eaton–Lambert syndrome may occasionally present as weakness in one extremity.
Muscle: It is unusual for the various forms of muscular dystrophy and dermatomyositis to present with monoplegia.
Approach to the Diagnosis
The neurologic examination will help determine the site of the lesion and thus the likely etiology. If there are hyperactive reflexes in the involved extremity, the lesion is probably in the upper spinal cord or cerebral cortex. If there is associated facial palsy or other cranial nerve signs, the lesion is probably in the brain or brainstem.
Hypoactive reflexes in the involved extremity indicate a lesion in the nerve roots, nerve plexus, or peripheral nerves. However, acute cerebral thrombosis, hemorrhage, or embolism may present with hypoactive reflexes in the involved extremity. Before proceeding with an expensive workup, a neurologist needs to be consulted.
Monoplegia of the upper extremities with hyperactive reflexes would indicate the need for an MRI or CT scan of the brain or cervical spinal cord. Monoplegia of the lower extremities with hyperactive reflexes would suggest the need for an MRI of the thoracic spine. However, a CT scan or MRI of the brain may still be required to rule out a parasagittal lesion.
Monoplegia with hypoactive reflexes may require an MRI or CT scan of the spine, electromyogram (EMG), and nerve conduction velocity (NCV) studies. Blood lead levels, glucose tolerance tests, and other studies indicated in a neuropathy workup may be required. Muscle biopsy and acetylcholine receptor antibody titers may be necessary.
Monoplegia is the paralysis of one extremity. Following the nerve impulse from the cerebral cortex down through the spinal cord, nerve roots, brachial and lumbosacral plexus, peripheral nerve, myoneural junction, and muscles allows us to recall the most significant causes of monoplegia.
Cerebral cortex: Monoplegia may result from a parasagittal tumor or abscess and anterior cerebral artery embolism or thrombosis. Occasionally an occlusion of the middle cerebral artery or its branches may cause monoplegia of the upper extremity, but there are almost always neurologic signs in the lower extremities in these cases.
Spinal cord: Early space-occupying lesions of the spinal cord and amyotrophic lateral sclerosis may present with monoplegia. It is unlikely for multiple sclerosis or transverse myelitis to present this way.
Nerve roots: Poliomyelitis, progressive muscular atrophy, and herniated discs may present with monoplegia. Early cauda equina tumors may present with monoplegia as well.
Brachial plexus: This would bring to mind brachial plexus neuropathy, thoracic outlet syndrome, and Pancoast tumors.
Sciatic plexus: This would suggest sciatic neuritis or injury.
Peripheral nerve: Trauma or entrapment of the peripheral nerves may present as a monoplegia. Charcot–Marie tooth disease may begin in one extremity.
Myoneural junction: Myasthenia gravis or Eaton–Lambert syndrome may occasionally present as weakness in one extremity.
Muscle: It is unusual for the various forms of muscular dystrophy and dermatomyositis to present with monoplegia.
Approach to the Diagnosis
The neurologic examination will help determine the site of the lesion and thus the likely etiology. If there are hyperactive reflexes in the involved extremity, the lesion is probably in the upper spinal cord or cerebral cortex. If there is associated facial palsy or other cranial nerve signs, the lesion is probably in the brain or brainstem.
Hypoactive reflexes in the involved extremity indicate a lesion in the nerve roots, nerve plexus, or peripheral nerves. However, acute cerebral thrombosis, hemorrhage, or embolism may present with hypoactive reflexes in the involved extremity. Before proceeding with an expensive workup, a neurologist needs to be consulted.
Monoplegia of the upper extremities with hyperactive reflexes would indicate the need for an MRI or CT scan of the brain or cervical spinal cord. Monoplegia of the lower extremities with hyperactive reflexes would suggest the need for an MRI of the thoracic spine. However, a CT scan or MRI of the brain may still be required to rule out a parasagittal lesion.
Monoplegia with hypoactive reflexes may require an MRI or CT scan of the spine, electromyogram (EMG), and nerve conduction velocity (NCV) studies. Blood lead levels, glucose tolerance tests, and other studies indicated in a neuropathy workup may be required. Muscle biopsy and acetylcholine receptor antibody titers may be necessary.
