Neuropathy in Lung Cancer

Introduction

There is a wide variety of neuromuscular diseases that impact patients with lung cancer and patients undergoing treatment for lung cancer. Neuropathy is a disease of peripheral nerves, with multiple primary, secondary, and tertiary consequences that can be debilitating for a patient's function and overall quality of life. For the purposes of this chapter, we will review the relationship of the neuropathic disease and function, various etiologies and their standard electrodiagnostic findings, clinical pearls for practical diagnostic evaluation. Finally, we will discuss management and current evidence for both treatment and rehabilitation.

Overview

The peripheral nerveous system includes the spinal roots, brachial or lumbosacral plexus, peripheral axons and/or myelin sheaths, the neuromuscular junction, and the muscle fibers. Anatomically, any level of the peripheral nervous system may be impacted by cancer and its treatment. The variety of mechanisms of injury and broad scope of clinical presentations makes it challenging to estimate the true incidence and prevalence of neuromuscular disorders in cancer patients. However, it is estimated that up to one-third of adult chronic cancer pain patients, across all tumor types and stages, are felt to have cancer-related neuropathic pain.

Cancer can directly affect the peripheral nervous system at any level via numerous mechanisms. Examples inlcude direct nerve compression or infiltration of the cancer itself (such as a Pancoast tumor compressing or infiltrating the brachial plexus or metastatic osseous disease of the spine causing radiculopathy), hematogenous or lymphatic spread, leptomeningeal dissemination, or perineural spread. Indirect effects from cancer include the body's immune response to cancer, such as paraneoplastic syndromes which often manifest with neuromuscular dysfunction (such as Lambert–Eaton Myasthenic Syndrome [LEMS]), or cancer-associated medical complications such as infections, weight loss, or malnutrition. Cancer treatment acquired neuropathies can result from effects of therapies, be it surgery (intercostal nerve injuries during thoracotomies or compressive neuropathies), chemotherapy (inducing peripheral neuropathy), radiation therapy, or immunologic therapy. Finally, patients may also have preexisting neurologic conditions, such as diabetic or hereditary neuropathies, or previous nerve injuries that can make the nerves more susceptible to cancer or its related treatments above.

Neuropathy has a wide variety of symptoms and presentations, ranging from pure sensory to pure motor, and from slight numbness and weakness in patients with chronic axonal neuropathy to significant loss of muscle strength including the respiratory muscles. Early recognition and accurate diagnosis is essential to proper treatment, rehabilitation and reduction of disability.

Neuropathy and Functional Consequences

Neuropathy can make one’s simple activities of daily living more challenging. An essential aspect of the rehabilitation treatment program for patients affected by lung cancer involves proper identification of the type of disease impairments and understanding of their primary, secondary, and tertiary consequences.

Disease is identified as a disorder of structure or function.

Impairment is a loss of normal function of part of the body.

Disability is when a person is not able to perform an activity in a normal way as a result of an impairment.

Handicap is when there are barriers that prevent a person with a disability from performing a role that is normal for that person. These limitations may be imposed by society, the environment, or by one's own attitude.

Neuropathy can result in different types of impairments depending on the type of nerves of nerves affected by the disease. Examples of this include the following:

• Disease of Sensory Nerves: This can cause impairments in sensation, such as with painful paresthesia, dysesthesia, cold sensitivity, tingling, numbness, alteration in vibration and proprioception, or a change in reflexes. Disability occurs, for example, when it impacts an individual's ability to shower, as standing and balancing, and temperature sensation in the shower is significantly impacted. Handicap would occur for example when an individual declines a social activity with friends due to the tremendous amount of effort required for self-hygiene.

• Disease of Motor Nerves: This can impair an individual's muscles and motion, such as muscle weakness or decreased coordination fine motor control. Disability can occur for example when it impacts one's ability to walk or when preparing food as opening cans or holding utensils to eat requires much more effort. Handicap would be if an individual were no longer able to perform their task at work due, such as a previously working full time hair dresser declining work due to weakness in her hands and no longer able to cut hair.

• Disease of Autonomic Nerves: This affects the autonomic regulation of internal organs and can cause impairments such as with orthostatic hypotension, constipation, urinary retention, irregular heart rate, and sexual dysfunction. Disability occurs, for example, when a patient's standing tolerance is severely impacted. An example of handicap from autonomic neuropathy would potentially be strained relationships due to sexual dysfunction or decreased ability to participate social activities due to limited standing tolerance.

When disease and injury cause an impairment, rehabilitation medicine is an essential aspect of care for the lung cancer patient, as early intervention, including prevention, identification, and treatment, can reduce the occurrence of functional limitations.

Neuropathy in the Cancer Patient

In the field of oncology, the etiology of neuropathy can be broken down into three categories: disease-related, cancer treatment-related, and patient-related. There may be a combination of several processes at once.