Unilateral arm numbness with radiation down the arm
Unilateral numbness that radiates down the arm can originate from cervical nerve root compression, peripheral nerve entrapment, brachial plexopathy, or central neurologic disease. [1] Unilateral arm numbness can also occur as part of a transient ischemic attack or stroke presentation and requires emergency assessment when acute neurologic deficits are present. [2]
Cervical radiculopathy (nerve root compression/irritation)
Cervical radiculopathy presents with arm numbness or paresthesia that follows a dermatomal distribution. [1] Symptoms may worsen with neck extension, rotation toward the symptomatic side, or overhead arm activity. [1] Objective neurologic findings may include dermatomal sensory loss, key myotome weakness, and asymmetric or diminished deep tendon reflexes. [1]
Thoracic outlet syndrome and other proximal peripheral nerve syndromes
Thoracic outlet syndrome can present with positional paresthesias that worsen with overhead activity and may be associated with vascular signs or diminished radial pulse. [1] Neuralgic amyotrophy (Parsonage–Turner syndrome) can present with acute severe shoulder pain followed by focal paresis. [1] Peripheral entrapments and plexopathies can mimic segmental weakness and are localized using detailed motor mapping and nerve conduction studies. [1]
Peripheral nerve entrapment syndromes
Carpal tunnel syndrome can produce hand paresthesias that worsen with hand activity and are often associated with nocturnal symptoms. [1] Ulnar neuropathy at the elbow (cubital tunnel) can cause numbness of the fourth and fifth digits and intrinsic hand weakness. [1] These entrapments can be distinguished from radiculopathy using sensory and motor patterns plus electrodiagnostic testing. [1]
Brachial plexopathy
Brachial plexus disorders can cause segmental motor and sensory deficits that may be mistaken for radiculopathy. [1] Localization distal to the foramen using nerve conduction studies and motor mapping supports a peripheral or plexus source rather than root-level pathology. [1]
Central nervous system causes (stroke, transient ischemic attack, demyelination)
TIA commonly presents with sudden onset unilateral weakness or numbness on one side of the body. [2] Because TIAs can be transient while still carrying early stroke risk, emergency assessment is recommended for sudden unilateral neurologic symptoms even when symptoms resolve. [2] Stroke and TIA symptoms include one arm weak or numb and require calling emergency services when present. [3]
Serious cervical spine etiologies (myelopathy, infection, malignancy)
Cervical myelopathy can present with hand clumsiness, gait instability, or urinary urgency and warrants prompt evaluation due to risk of progressive neurologic impairment. [1] Red-flag features for serious spinal etiologies include fever, night sweats, unexplained weight loss, immunosuppression, persistent pain at rest, and tenderness over the vertebrae. [1]
Herpes zoster (shingles) radicular-pattern neuropathy
Herpes zoster can cause dermatomal sensory symptoms that may be experienced as unilateral numbness or paresthesia radiating along a sensory distribution. [1]
Key clinical pattern features supporting localization
Dermatomal patterning with provocation by specific neck movements supports cervical radiculopathy. [1] Positional symptoms linked to overhead activity with possible vascular features supports thoracic outlet syndrome. [1] Digit-specific sensory and intrinsic muscle weakness patterns support targeted peripheral entrapment such as carpal tunnel or cubital tunnel. [1] Sudden onset unilateral arm numbness with other neurologic deficits supports evaluation for TIA or stroke. [2]
Emergency indications
Sudden onset one-arm numbness or weakness should be treated as a possible stroke/TIA presentation requiring emergency assessment. [2] Calling emergency services is recommended when stroke warning signs are present, including one arm weak or numb with facial droop or speech difficulty. [3]