Monoparesis

Monoparesis is the weakness of a single limb, typically resulting in reduced muscle strength without complete paralysis. It is distinguished from monoplegia, in which there is complete loss of motor function in one limb. Monoparesis can involve an arm or a leg and may be due to central nervous system or peripheral causes.

Common etiologies include focal central nervous system lesions such as stroke (ischemic or hemorrhagic) affecting the corticospinal pathways, brain or spinal cord injuries, tumors, or demyelinating diseases. Peripheral causes include isolated nerve injuries or neuropathies (for example, radial, peroneal, or ulnar nerve palsies), brachial plexus injuries, and neuromuscular disorders that affect only one limb. In some cases, inflammatory or infectious processes can produce unilateral weakness.

Clinical features vary with the site of injury. The limb shows weakness on attempted movement, with tone and reflex changes that reflect the underlying lesion (spasticity with upper motor neuron lesions; flaccidity in acute phases or with lower motor neuron lesions). Sensory symptoms may accompany motor weakness, depending on the lesion.

Evaluation relies on a focused neurological examination and targeted imaging. In suspected central causes, MRI of the brain and spinal cord is often essential, with CT used acutely for stroke. Electromyography and nerve conduction studies help distinguish peripheral nerve or root lesions from central causes. Laboratory tests may aid in identifying metabolic or inflammatory contributors.

Management targets the underlying cause. Acute stroke requires reperfusion therapy when eligible, supportive care, and rehabilitation. Peripheral nerve or brachial plexus injuries are managed with physical and occupational therapy, splinting, and sometimes surgical intervention. Prognosis depends on etiology, extent of injury, and timely, multidisciplinary rehabilitation.