Hand palsy, characterized by weakness, involuntary movement, or loss of function in the hand, is a symptom of an underlying issue within the nervous or muscular systems. Determining the precise cause is necessary because treatment for a problem originating in the brain is vastly different from that for a compressed nerve in the wrist. Dysfunction anywhere along the pathway, from the brain to the muscle fibers, can lead to the impaired function known as palsy.
Defining Hand Palsy and Related Symptoms
The term “palsy” describes a significant loss of motor control, encompassing both complete paralysis (plegia) and partial weakness (paresis). Physicians often use it interchangeably with these terms. Symptoms of hand palsy frequently include profound weakness, diminished grip strength, and a loss of dexterity, making fine motor tasks nearly impossible.
Hand palsy must be distinguished from movement disorders like tremor, which is an involuntary, rhythmic muscle movement. Tremors are distinct neurological issues, such as the resting tremor of Parkinson’s Disease or the action tremor of Essential Tremor. Palsy, conversely, primarily reflects a problem with the strength or ability to initiate movement. It is often accompanied by changes in muscle tone, such as stiffness or flaccidity.
Neurological Causes Originating in the Central Nervous System
Hand palsy stemming from the Central Nervous System (CNS)—the brain and spinal cord—involves damage to the upper motor neurons (UMNs). These neurons originate in the motor cortex and travel down to the spinal cord, acting as the primary messengers for voluntary movement. Damage to this pathway interrupts the signal before it reaches the nerves that connect directly to the hand muscles.
A stroke, caused by interrupted blood supply to the brain, is a frequent cause of UMN damage, particularly when the motor cortex is affected. Damage often results in weakness or paralysis on the opposite side of the body (hemiparesis or hemiplegia), significantly impairing hand function. This weakness is often accompanied by spasticity, a velocity-dependent muscle stiffness that occurs because UMNs can no longer inhibit spinal cord reflexes.
Cerebral Palsy (CP) is another CNS cause, arising from damage to the developing brain before, during, or shortly after birth. The most common form, spastic CP, is a UMN disorder that leads to weakness and spasticity in the arm and hand (spastic hemiplegia). Similarly, Multiple Sclerosis (MS) can cause hand palsy when autoimmune inflammation creates lesions on UMNs within the brain or spinal cord. This demyelination disrupts nerve signals, resulting in muscle weakness and coordination issues.
Causes Stemming from Peripheral Nerve Damage
When hand palsy results from a problem outside the CNS, the cause lies in the peripheral nervous system, involving the lower motor neurons or the nerves extending into the limbs. These peripheral nerve palsies, or neuropathies, are often caused by mechanical compression, trauma, or systemic diseases that directly damage the nerve structure.
Entrapment neuropathies are common, occurring when a nerve is physically compressed in a narrow space. Carpal Tunnel Syndrome, the most frequent example, involves compression of the median nerve at the wrist, leading to weakness in the thumb muscles and diminished grip and pinch ability. Ulnar Nerve entrapment, often at the elbow (cubital tunnel), results in weakness of the small muscles of the hand, affecting grip strength and finger coordination.
Trauma can cause immediate palsy by lacerating or crushing a nerve, such as a deep cut or a bone fracture. Radial nerve palsy, sometimes called “Saturday night palsy,” is a specific nerve injury caused by prolonged external pressure on the nerve along the arm. This injury causes “wrist drop,” paralyzing the muscles responsible for extending the wrist and fingers. Generalized peripheral neuropathies, frequently seen in individuals with long-standing diabetes, can also cause symmetrical hand weakness and sensory loss due to widespread nerve damage.
Systemic and Musculoskeletal Contributors
Palsy-like symptoms can arise from issues not strictly neurological, involving the muscles themselves or the body’s chemical balance. Myopathies are disorders where the primary problem is dysfunction within the muscle fibers, impairing their ability to contract despite receiving proper nerve signals. While many myopathies, such as Muscular Dystrophy, typically cause proximal weakness, some forms can affect the distal muscles of the hands, leading to reduced strength.
The body’s internal chemistry plays a significant role in muscle and nerve function, meaning severe systemic imbalances can manifest as weakness. Electrolytes like potassium, calcium, and magnesium are necessary for regulating muscle contraction and nerve signaling. An imbalance, such as low potassium (hypokalemia), can cause generalized muscle weakness, spasms, and even paralysis affecting the hands. Chronic conditions like kidney failure or thyroid disease can indirectly contribute to hand weakness by causing fluid retention and electrolyte disturbances that damage peripheral nerves. Certain toxic exposures, notably heavy metals like lead, can also poison the nervous system, resulting in a peripheral neuropathy that presents as hand palsy.