Signs and symptoms of paraneoplastic syndromes of the nervous system can develop relatively quickly, often over days to weeks. Signs and symptoms of paraneoplastic syndromes of the nervous system often begin even before a cancer is diagnosed.

Signs and symptoms vary depending on the body part being injured, and may include:

• Difficulty walking
• Difficulty maintaining balance
• Loss of muscle coordination
• Loss of muscle tone or weakness
• Loss of fine motor skills, such as picking up objects
• Difficulty swallowing
• Slurred speech or stuttering
• Memory loss and other thinking (cognitive) impairment
• Vision problems
• Sleep disturbances
• Seizures
• Hallucinations
• Unusual involuntary movements

Types of paraneoplastic syndromes

Examples of paraneoplastic syndromes of the nervous system include:

• Cerebellar degeneration. This is the loss of nerve cells in the area of the brain that controls muscle functions and balance (cerebellum). Signs and symptoms may include unsteady or impaired walking, lack of muscle coordination in your limbs, inability to maintain your trunk posture, dizziness, nausea, involuntary eye movement, double vision, difficulty speaking, or difficulty swallowing.
• Limbic encephalitis. This is inflammation affecting a region of the brain known as the limbic system, which controls emotions, behaviors and certain memory functions. People with this disorder may experience personality changes or mood disturbances, memory loss, seizures, hallucinations, or drowsiness.
• Encephalomyelitis. This syndrome refers to inflammation of the brain and spinal cord. There may be a wide variety of symptoms and signs depending on the area affected.
• Opsoclonus-myoclonus. This syndrome is due to dysfunction of the cerebellum or its connections. It can cause rapid, irregular eye movements (opsoclonus) and involuntary, chaotic muscle jerks (myoclonus) in your limbs and trunk.
• Stiff person syndrome. Previously called stiff man syndrome, this syndrome is characterized by progressive, severe muscle stiffness or rigidity, mainly affecting your spine and legs. It may also cause painful muscle spasms.
• Myelopathy. This term refers to a syndrome of injury limited to the spinal cord. Depending on the level of spinal cord injury, you may have changes in bowel and bladder function, and severe weakness and numbness up to a certain level in your body. If the level of injury includes your neck, you can have severe disability affecting all four limbs.
• Lambert-Eaton myasthenic syndrome. This is a syndrome caused by disrupted communication between nerves and muscles. Signs and symptoms include pelvic and lower extremity muscle weakness, fatigue, difficulty swallowing, difficulty speaking, irregular eye movement, and double vision. Autonomic nervous system problems can include dry mouth and impotence.

When it occurs as a paraneoplastic syndrome, Lambert-Eaton myasthenic syndrome is typically associated with lung cancer.

• Myasthenia gravis. Myasthenia gravis is also related to disrupted communication between nerves and muscles and also characterized by weakness and rapid fatigue of any of the muscles that are under voluntary control, including muscles in your face, eyes, arms and legs. The muscles involved in chewing, swallowing, talking and breathing may be affected as well.

When myasthenia gravis occurs as a paraneoplastic syndrome, it is typically associated with cancer of the thymus gland (thymoma).

• Neuromyotonia. Neuromyotonia — also known as Isaacs' syndrome — is characterized by abnormal impulses in nerve cells outside the brain and spinal cord (peripheral nerve hyperexcitability) that control muscle movement. These impulses can cause twitching, muscle rippling that looks like a "bag of worms," progressive stiffness, muscle cramps, slowed movement and other muscle impairments.
• Peripheral neuropathy. This condition refers to patterns of damage to nerves that transmit messages from the brain or spinal column to the rest of your body. When damage involves only the sensory nerves of the peripheral nervous system, you can have pain and disturbances in sensation anywhere in your body.
• Dysautonomia. Dysautonomia refers to a wide range of signs and symptoms resulting from injury to the nerves that regulate nonvoluntary body functions (autonomic nervous system), such as heart rate, blood pressure, sweating, and bowel and bladder functions. When this part of the nervous system is affected, common symptoms are low blood pressure, irregular heartbeats and trouble breathing.

Paraneoplastic syndromes are not caused by cancer cells directly disrupting nerve function, by the cancer spreading (metastasis), or by other complications such as infections or treatment side effects. Instead, they occur alongside the cancer as a result of the activation of your immune system.

Researchers believe paraneoplastic syndromes are caused by cancer-fighting abilities of the immune system, particularly antibodies and certain white blood cells, known as T cells. Instead of attacking only the cancer cells, these immune system agents also attack the normal cells of the nervous system and cause neurological disorders.

Any cancer may be associated with a paraneoplastic syndrome of the nervous system. However, the disorders occur more often in people with cancers of the lung, ovary, breast, testis or lymphatic system.