The Neurological Complications of Medical Disease

Neurologists frequently evaluate patients with neurological symptoms and signs occurring in the context of an underlying medical illness; the neurological illness may be the presenting feature of a yet-undiagnosed medical illness or may be a complication of a known systemic disease or its treatment. Despite the limited training of most neurologists in internal medicine (typically limited to a one year “preliminary” medicine internship), neurologists need to be aware of the many systemic illnesses—and their therapies—that can be associated with neurological manifestations.[1] With a firm knowledge of these associations, the neurologist can be an active and important participant in the recognition, diagnosis, and management of both the neurological syndrome and the causative systemic condition.

In this issue of Seminars in Neurology, I have asked Faculty to address various categories of neurological dysfunction and discuss the medical illnesses that can cause this dysfunction. Therefore the articles in this issue don't have specific medical diseases or medical syndromes in their title; rather, they're categorized by gross neurological localization (e.g., peripheral nerve, muscle, visual system) or symptom or sign (e.g., movement disorder, encephalopathy, and stroke). Each article's authors address systemic (“medical”) diseases—and in many cases, their treatments—that cause neurological symptomatology referable to these neurological categories. This way of looking at the neurological complications of medical disease (exemplified by Layzer's classic text on the Neuromuscular Manifestations of Systemic Disease,[2] an influential text for me during my training) especially parallels the common scenario where the medical illness underlying the neurological syndrome is unknown; or when a patient is on several medications for a systemic illness but which drug is causing toxicity is not entirely clear.

The first article, by Drs. Brandon Barton, Elizabeth Zauber, and Christopher Goetz, reviews the many movement disorders that occur due to medical disease or toxicity. By grouping the topics in their article into the four prototypic movement disorders of parkinsonism, non-parkinsonian tremor, dystonia, and chorea, the authors have created a nice road map for the clinical evaluation of patients whose abnormal movements may be related to medical disease or drug toxicity. Dr. Janet Rucker next reviews the many neuro-ophthalmological symptoms and signs that can occur from systemic disease or its treatment. Her clarity of writing is mirrored by the outstanding and carefully chosen images that illustrate her paper to provide us with an update on the many systemic conditions that affect the optic nerves, intracranial visual pathways, and eye movements. Next, Dr. Hannah Briemberg provides a very clear discussion of many medical conditions that present with dysfunction of the peripheral nerves, anywhere from the cell body to the terminal axon; each section of this thorough article includes a helpful summary of the treatment of many of the peripheral nerve manifestations of medical disease that the neurologist may encounter.

Struck by how often we are asked to see patients with diffuse encephalopathies (delirium) due to medical illness—many of whom have a cause of encephalopathy beyond the “usual suspects” of uremic or hepatic encephalopathy or encephalopathy due to sedative drugs or electrolyte imbalance—Dr. Allison Weathers and I felt it was important to discuss encephalopathy because this is one of the most common reasons for neurological consultation on inpatients. We address the seemingly rare, but probably actually not so unusual, potentially treatable causes of diffuse encephalopathy that should be considered when assessing the encephalopathic patient, to attempt to avoid prolonged dysfunction or irreversible neurological injury. Next, although medical conditions such as hypertension, dyslipidemia, and heart disease are well-known risk factors for stroke, Dr. Michael Chen discusses many of the other systemic processes that should be kept in the differential diagnosis—and excluded when appropriate—for patients who present with stroke, particularly when presenting outside of the typical age- and risk-factor milieu. Finally, Drs. Madhu Soni and Anthony Amato discuss the many medical illnesses and medications that can result in myopathic complications. This article will serve as a very practical reference to the clinician dealing with patients with myopathic dysfunction from systemic disease, ranging from asymptomatic elevations in serum muscle enzymes to severe muscle weakness and rhabdomyolysis.

Not all neurological presentations of medical illness can be covered in one volume; however, I hope that busy clinical neurologists will find the articles in this issue of Seminars in Neurology instructive and practical as they care for patients with neurological signs and symptoms in both inpatient and outpatient settings in the context of medical illness, whether diagnosed or undiagnosed.

Finally, I'd like to sincerely thank Karen Roos, M.D. for her confidence in inviting me to be the Guest Editor for this issue, and for her wonderful and truly expert guidance and encouragement throughout this project.

REFERENCES

• 1 Aminoff M J. Training in neurology.  Neurology. 2008;  70(20) 1912-1915
• 2 Layzer R B. Neuromuscular Manifestations of Systemic Disease. Philadelphia; FA Davis Co 1985