Cerebral infarction, cerebral hemorrhage, and brain tumors can become infected. The development of abscess in a brain lesion is typically delayed after the stroke presentation. Often septicemia due to an infected indwelling urinary bladder catheter is the source. Sometimes infection can develop in a previously asymptomatic brain tumor of any type.

In the era of MRI we have advanced our knowledge of the topography of Wernicke disease. We have learned that cortical and striatal lesions can occur. Clinical observations have revealed that hearing loss can occur, sometimes with the MRI correlate of involvement of the inferior colliculi. Vestibular signs have been correlated with involvement of the vestibular nuclei. Previously unpublished data show a high incidence of the midline cerebellar lesion in oropharyngeal cancer. Ideas about proper thiamine dosing are discussed.

The neuropathology of Wilson disease resembles that of chronic nonfamilial hepatocerebral disease. The neurological features of the hereditary disease also resemble those of the nonfamilial disease. Liver transplantation improves both the lesions on MRI scans and the neurologic disorder of Wilson disease. For these reasons and others there is no reason to invoke copper toxicity in the pathogenesis of Wilsonian hepatocerebral disease.

Quasi-neurological problems can be spurious, the product of the mind or emotions. Distinguishing such conditions from coarse brain disease is accomplished by systematic neurologic analysis. Many of these patients are depressed or malingering. Intense emotions may account for other cases. In a given patient more than one of these terms may be applicable.

Asterixis is typically an asymptomatic clinical sign of encephalopathy which occurs symmetrically but asynchronously on the two sides of the body. Unilateral or asymmetric asterixis can occur under special circumstances. The arrhythmic lapses of sustained posture are due to episodic cessation of myoelectrical activity.

Aphasia, apraxia, and agnosia are terms we use to describe clinical abnormalities. Each term is applied to a variety of neurologic disorders. In a given case more than one of the terms could be appropriate to describe the deficit. The phenomena to which these words are applied have no uniform patho-anatomic basis.

Transneuronal effects distant from acute brain lesions are called diaschisis. Examples are spinal shock and hyporeflexia after acute stroke. Pathological effects distant from chronic brain lesions are anterograde and retrograde transneuronal atrophy. This atrophy is best seen in the visual and cerebro-cerebellar systems, but it almost certainly occurs in other regions of the cerebral cortex. The mechanism of transneuronal trophism is not fully understood.

Individual susceptibility, regional vulnerability, and vascular supply are among the variables which determine the distribution of the brain injury in ischemic hypoxic encephalopathy. Also varied are the clinical manifestations which range from transient encephalopathy to “brain death.” Severe encephalopathies can entangle physicians and hospitals in civil and criminal proceedings.

In the upper motor neuron syndrome, there are abnormalities of spinal reflexes. The disordered monosynaptic muscle stretch reflex is manifest by a velocity dependent increase in muscle tone and exaggerated tendon jerks. The cutaneous reflex to plantar stimulation is abnormal in that plantar flexion of the great toe is lost. Disinhibition of the polysynaptic spinal flexion reflex is responsible for the Babinski sign and the clasp-knife phenomenon.

The grasp reflex and the instinctive grasp response differ in their necessary stimulus, level of motor integration, and clinical utility. The grasp reflex proper results from a combined cutaneous and proprioceptive stimulus. It is a stereotyped reflex due to disease of the supplementary motor area of the contralateral frontal lobe. More complex is the instinctive grasp response which involves groping. Its stimulus is purely tactile. A different phenomenon is the alien hand syndrome in which the hand has a will of its own.

Various infectious agents invade brain and spinal fluid through the olfactory nerves and bulbs. The best example is the amoeba Naegleria which usually enters the nose during recreation in fresh water. Strong epidemiologic, pathologic, and experimental evidence support this transolfactory route of neurologic infection. Viruses can also cause meningioencephalitis via transolfactory spread.

Vibration sense is not affected by disease in the posterior columns of the spinal cord. The idea that they are related to sensing vibration originated with the study of tabes dorsalis, subacute combined degeneration of the spinal cord, and Friedreich’s ataxia. More modern studies of patients with cordotomy and syringomyelia disprove the belief that vibration sense is carried by the posterior columns. Vibration sensing is accomplished in the phylogenetically old thalamus.

The term “limbic system” refers to structures between the hypothalamus and the neocortex. It originated as a speculation that many structures were a unit which was the basis of emotion. This theory was Paul MacLean’s elaboration of James Papez’s idea. In retrospect, as a system, the entity does not exist.

Inability to learn and remember out of proportion to all other cognitive deficits is the amnesic syndrome. It is typically caused by bilateral damage to one of four areas, the hippocampus, medial thalamus, basal forebrain, or fornix.

Raymond Adams recognized a patient as having a clinically unique disease. On autopsy the brain revealed unique neuropathology. On microscopy Byron Waksman, an immunologist, noted inclusion bodies in oligodendroglia. Astrom, Mancall, and Richardson named the entity Progressive Multifocal Leukoencephalopathy (PML). Gabriele Zu Rhein and Sam Chou used electron microscopy to demonstrate virus in the cells. Later Zu Rhein provided fresh brain to Druard Walker. He and Billie Padgett grew the virus in cell culture to prove that PML was in fact a viral disease. These many investigators contributed to the early understanding of this disease.