Multiple myeloma is a form of blood cancer characterized by the abnormal proliferation of plasma cells in the bone marrow. A frequent complication of this disease and its treatments is nerve damage, known as peripheral neuropathy. Up to 20% of people exhibit symptoms at diagnosis, and the prevalence of neuropathy increases substantially during cancer treatment. This nerve damage can diminish quality of life by interfering with everyday functions.
Causes of Neuropathy in Multiple Myeloma
Nerve damage in patients with multiple myeloma stems from the disease itself or from its therapies. The cancer’s own mechanisms can lead to neuropathy when malignant plasma cells produce M protein, which is directly harmful to nerve cells. This protein may contribute to the erosion of the myelin sheath, the protective layer that insulates nerves, leading to the degradation of nerve cell axons. In some instances, tumors formed by myeloma cells can physically compress nerves, particularly those exiting the spinal cord.
More commonly, neuropathy is a side effect of the treatments for multiple myeloma, a condition called chemotherapy-induced peripheral neuropathy (CIPN). Specific classes of drugs are frequently implicated, including proteasome inhibitors like bortezomib and immunomodulatory drugs such as thalidomide and lenalidomide. These medications, while effective at killing cancer cells, can also damage peripheral nerves. For example, proteasome inhibitors cause a buildup of proteins within cells, which leads to the death of both cancer cells and healthy nerve cells.
Common Symptoms and Their Impact
Neuropathy in multiple myeloma presents with sensory, motor, and autonomic symptoms. Sensory symptoms are the most prevalent and often the first to appear. Patients frequently report sensations of numbness, tingling, or a “pins and needles” feeling, typically starting in the feet and hands. Some individuals experience a burning or freezing sensation, and a diminished ability to sense temperature changes, which can create hazards during daily activities.
Motor symptoms involve muscle function and can significantly affect mobility and dexterity. This may present as weakness in the limbs, causing difficulties with balance and walking. Fine motor skills can also be compromised, making tasks such as buttoning a shirt or writing a note challenging. The feeling of wearing gloves or socks when none are present is another common description of the altered sensation.
Autonomic symptoms, which relate to the nerves that control involuntary bodily functions, are less common but can occur. These might include dizziness upon standing, a result of changes in blood pressure regulation. Issues with bowel or bladder control can also be a manifestation of autonomic neuropathy.
How Neuropathy is Diagnosed
A diagnosis of neuropathy in a multiple myeloma patient involves a thorough review of their medical history and a detailed physical and neurological examination. The physician will inquire about the specific nature, location, and timing of the symptoms. During the neurological exam, reflexes, muscle strength, and the ability to perceive different sensations are tested to identify any deficits.
To gain a more objective measure of nerve function, specialized tests are often employed. Nerve conduction studies (NCS) are used to assess the speed and strength of electrical signals as they travel through the nerves. This test can help determine if the protective myelin sheath or the nerve axon itself is damaged. Electromyography (EMG) is another test that evaluates the electrical activity of muscles, providing insight into the nerve supply to those muscles. Together, these tests help clinicians understand the extent and type of nerve damage.
Approaches to Managing Neuropathic Pain
Managing neuropathy in multiple myeloma often starts with adjustments to the cancer treatment itself, since certain chemotherapy drugs are a primary cause. This could involve reducing the dose of the neurotoxic drug, changing the frequency of its administration, or switching to an alternative medication. These decisions are made to balance the need for effective cancer control with the goal of minimizing side effects.
Various medications can also be prescribed to alleviate the symptoms of neuropathic pain. Unlike standard pain relievers, these drugs target the specific nerve-related pain mechanisms. Certain types of antidepressants, such as duloxetine, and anticonvulsant medications, like gabapentin, have been shown to be effective in reducing the burning, tingling, and pain associated with neuropathy. For localized symptoms, topical treatments may also provide relief.
Physical therapy can help maintain muscle strength, improve balance, and support mobility. Occupational therapy can assist patients in adapting to changes in fine motor skills, offering strategies and tools to accomplish daily tasks. Simple, practical measures like wearing comfortable, supportive footwear and inspecting the feet daily for injuries that might go unnoticed due to numbness are important self-management techniques. Some patients may also explore complementary therapies like acupuncture, which has been found to help improve symptoms.