Shaking is a common symptom for individuals navigating cancer treatment, but it manifests as several distinct involuntary movements. Tremors are rhythmic, oscillatory movements affecting body parts like the hands, arms, or legs. Rigors are intense, uncontrolled muscular contractions associated with a rapidly rising body temperature or fever. Myoclonus presents as sudden, brief, shock-like jerks of a muscle or muscle group. The underlying causes are numerous, stemming from the malignancy itself, cancer treatments, or secondary systemic complications.
Neurological Impact of Cancer
The physical presence of a tumor can directly interfere with the central or peripheral nervous system, leading to various movement disorders. A mass lesion, especially within the brain, can compress or invade areas that regulate motor control, such as the cerebellum or the basal ganglia. Tumors in the cerebellum, which coordinates voluntary movements, often result in an intention tremor, where shaking becomes more pronounced during a purposeful action, like reaching for an object.
Tumors near the basal ganglia, structures involved in initiating and controlling movement, can cause parkinsonism, which includes a resting tremor. While brain tumors causing movement disorders are relatively uncommon, their location determines the type of shaking experienced.
The cancer can also indirectly trigger a neurological response known as a Paraneoplastic Syndrome (PNS). PNS occurs when the immune system generates antibodies to fight the cancer that mistakenly cross-react with healthy nervous tissue. This autoimmune attack leads to inflammation and dysfunction in the brain, spinal cord, or peripheral nerves. This can result in cerebellar ataxia, characterized by uncoordinated movement and tremors, or paraneoplastic myoclonus, presenting as sudden, irregular jerks.
Treatment-Induced Shaking
Medical interventions designed to eliminate cancer cells can inadvertently damage the nervous system, resulting in iatrogenic movement disorders. Chemotherapy-Induced Peripheral Neuropathy (CIPN) is a common side effect where neurotoxic drugs, such as platinum-based agents or vinca alkaloids, injure the peripheral nerves. This nerve damage often manifests as a tremor affecting the hands and feet, or as a loss of fine motor control.
Specific chemotherapies like cytarabine, thalidomide, and high-dose regimens are known to cause tremors or cerebellar toxicity. Newer targeted therapies and immunotherapies can also induce shaking. Immune checkpoint inhibitors (ICIs) occasionally result in overactive immune cells attacking nervous tissue, leading to immune-related neurological toxicity and tremors that may be delayed in onset.
Certain anti-nausea medications (antiemetics), such as metoclopramide, can cause extrapyramidal side effects, including acute dystonic reactions and drug-induced parkinsonism. High-dose corticosteroids, frequently used to manage inflammation or brain swelling, can also contribute to a noticeable action tremor. The risk of these movement disorders depends on the cumulative dose of the drug, the patient’s age, and pre-existing neurological conditions.
Systemic and Metabolic Factors
Shaking can also be a symptom of broader systemic disturbances that disrupt the body’s internal balance. Rigors, which are whole-body shaking episodes, commonly present with infection, sepsis, or a sudden rise in body temperature. These episodes are the body’s attempt to generate heat to raise its core temperature and are distinct from the rhythmic movements of a tremor.
Metabolic abnormalities, often seen in cancer patients due to the disease or malnutrition, can trigger neurological symptoms. Dysregulation of blood sugar, such as hypoglycemia, can lead to shakiness and tremors. Imbalances in electrolytes like low magnesium or calcium levels can also increase nerve and muscle excitability, resulting in twitching or myoclonic jerks.
The profound muscle wasting condition known as cancer cachexia is a major systemic factor. Cachexia involves the loss of skeletal muscle mass, accompanied by severe fatigue and weakness. This physical weakness can make simple tasks difficult, leading to shaky or unstable movements when the patient attempts to exert themselves. An overactive thyroid gland can also be a contributing factor that presents as a noticeable tremor.