The nervous system, a complex network comprising the brain, spinal cord, and peripheral nerves, orchestrates virtually all bodily functions. Cancer, characterized by uncontrolled cell growth, can profoundly disrupt this intricate system, leading to various neurological issues. These effects can stem directly from the cancer’s presence or indirectly from its treatments.
Tumor Growth and Compression
Primary tumors originating within the brain or spinal cord directly interfere with nervous system function. Tumors such as gliomas (from glial cells) or meningiomas (from protective membranes) can occupy space, displace, or destroy healthy neural tissue. This physical presence disrupts normal electrical signaling and cellular processes.
Tumors located elsewhere in the body can also exert neurological effects by growing large enough to compress nearby nerves or the spinal cord. For instance, a lung tumor might press on nerves in the arm, leading to pain, numbness, or weakness in that limb. Similarly, tumors in the spine can compress the spinal cord, potentially causing severe pain, muscle weakness, loss of sensation, or problems with bladder and bowel control.
The specific neurological symptoms associated with direct tumor impact depend on the tumor’s location. A brain tumor in the motor cortex might cause weakness on one side of the body, while a tumor in the temporal lobe could lead to seizures or speech difficulties. Headaches, often persistent and worsening, can result from increased pressure within the skull. Vision changes, balance issues, and cognitive impairments like memory problems or confusion are common.
Cancer Spread and Immune Responses
Metastasis is when cancer cells travel from their original site to establish new tumors in distant parts of the body. When cancer metastasizes to the nervous system (brain, spinal cord, or peripheral nerves), these new growths can cause significant neurological dysfunction. Lung, breast, and melanoma cancers are among the most common types that spread to the brain.
Metastatic tumors within the nervous system produce symptoms similar to primary tumors, including focal deficits like weakness or numbness, seizures, headaches, or cognitive changes. Multiple metastatic lesions can lead to widespread and complex neurological impairments. The rapid growth of these secondary tumors can quickly overwhelm the nervous system, leading to acute neurological emergencies.
Paraneoplastic syndromes are a distinct and often rare category of neurological complications where the body’s immune system mistakenly attacks parts of the nervous system in response to a distant cancer. Cancer cells produce substances that trigger an immune response, and the activated immune cells or antibodies then cross-react with healthy nervous system tissues. The cancer itself is not physically present in the affected nervous system areas.
Symptoms of paraneoplastic syndromes can include cerebellar ataxia (problems with coordination and balance) or limbic encephalitis (memory issues, confusion, and seizures). Myasthenia gravis-like symptoms, characterized by muscle weakness that worsens with activity, can also occur. These neurological dysfunctions can sometimes appear before the primary cancer is diagnosed, making them an important clue for early detection.
Treatment-Induced Neurological Changes
Cancer treatments, while targeting cancerous cells, can also lead to neurological complications. Chemotherapy often causes chemotherapy-induced peripheral neuropathy (CIPN), affecting nerves in the hands and feet. This can manifest as numbness, tingling, pain, or weakness, significantly impacting daily activities. “Chemo brain,” or cognitive impairment, characterized by difficulties with concentration, memory, and multitasking, is another common side effect.
Radiation therapy, particularly when directed at the brain or spine, can induce immediate and delayed neurological effects. Acutely, patients might experience swelling, fatigue, or headaches due to transient inflammation. Delayed effects can emerge, including radiation necrosis (where healthy tissue dies) or cognitive decline, impacting memory and processing speed. Radiation myelopathy, a rare but severe complication, involves damage to the spinal cord, leading to weakness, sensory loss, or paralysis.
Surgical removal of tumors, especially those near or within the nervous system, carries risks of nerve damage or functional deficits. Brain tumor surgery might result in new or worsened neurological impairments depending on the tumor’s location and extent of resection. Peripheral nerve damage can occur during other surgeries if nerves are inadvertently cut, stretched, or compressed.
Immunotherapy, a newer class of cancer treatments, harnesses the body’s immune system to fight cancer, but it can also lead to immune-related adverse events (irAEs) affecting the nervous system. The activated immune system, while targeting cancer cells, can sometimes attack healthy neural tissues. This can result in conditions like encephalitis (brain inflammation) or various forms of neuropathy, causing nerve damage and dysfunction.