Migraine with aura: This condition can cause transient neurological symptoms, including upper extremity weakness, which may lead to dropping items. The paroxysmal nature of the symptoms fits with the episodic pattern of migraines.

Epilepsy (partial seizures): Focal seizures can cause localized weakness, including in the upper extremities, leading to a sudden inability to hold items. The paroxysmal onset and offset are characteristic of seizure activity.
Transient ischemic attack (TIA): TIAs, or "mini-strokes," can cause sudden, temporary weakness in parts of the body, including the upper extremities, resulting in dropped items. The transient nature of TIAs aligns with the paroxysmal description.
Multiple sclerosis: This chronic condition can cause a wide range of neurological symptoms, including weakness, which can be episodic and affect the upper extremities, potentially causing items to be dropped.

Subclavian steal syndrome: This condition, caused by stenosis or occlusion of the subclavian artery, can lead to transient weakness or numbness in the arm, especially with exercise, due to "stealing" of blood flow. It's crucial to diagnose to prevent potential stroke.
Thoracic outlet syndrome: Compression of the nerves or blood vessels that pass into the thoracic outlet can cause episodic weakness, numbness, or tingling in the upper extremities, potentially leading to dropping items. Early diagnosis can prevent long-term damage.
Cervical spine instability or disc disease: Conditions affecting the cervical spine can cause episodic upper limb weakness due to compression of the spinal cord or nerve roots, which is critical to identify to prevent permanent neurological damage.

Mitochondrial myopathies: These are a group of disorders that affect the mitochondria, often causing muscle weakness that can be episodic. While rare, they should be considered in the differential diagnosis, especially if other symptoms such as myalgias or exercise intolerance are present.
Periodic paralysis: A group of rare genetic disorders that lead to episodic muscle weakness, which can affect the upper extremities and cause patients to drop items. The weakness can be triggered by various factors, including rest or exercise after meals.
Neuromuscular junction disorders (e.g., myasthenia gravis): These conditions can cause fluctuating muscle weakness that worsens with activity and improves with rest. While not typically described as paroxysmal, they can cause significant weakness in the upper extremities, leading to dropped items.