The Neurologic System

Chapter 19 The Neurologic System





Generalities


In times of magnetic resonance imaging (MRI) and computed tomography (CT), the neurologic exam may seem almost anachronistic. Yet, as the leading British neurologist McDonald Critchley (1900–1997) once said during one of his U.S. visits, “CT scanning will take away the shadows of neurology, but the music will still remain.” Indeed, the neurologic exam remains the most sophisticated part of physical diagnosis, still able to pinpoint the location of a lesion (“history tells you what it is, but the exam tells you where it is”). Of course, good skills, plus mastering of neuroanatomy and neurophysiology are a prerequisite. This chapter will highlight the essentials. But all sections are worthwhile.





A. Mental Status Examination



















(1)Language


















B. Cranial Nerves Examination







38 What abnormal eye movements result from damage to CN III, IV, or VI?




image The oculomotor supplies medial, superior, and inferior rectus; inferior oblique; and levator palpebrae (which raises the eyelid). It also contains parasympathetic fibers that constrict the pupil. Hence, its lesions result in a partially abducted eye that is difficult to adduct, raise, or lower. In fact, it is frequently turned out (exotropia). There also is a drooping eyelid (ptosis) and a pupil that may be larger (mydriatic) and difficult to constrict. In more subtle cases, there may only be diplopia or blurred vision. A CN III palsy that spares the pupils (i.e., ptosis, and external rotation of the globe, but symmetric and equally reactive pupils) suggests diabetes, but also vasculitides and multiple sclerosis.


image The trochlear supplies the superior oblique muscle by extending over a trochlea, or pulley. Since this nerve allows us to view the tip of our nose, its lesion will result in an eye that cannot be depressed when adducted. Hence, whenever patients pull their eyes inward (toward the nose), they will be unable to move them downward. This is often subtle. An isolated right superior oblique paralysis results in (1) exotropia to the right (R); (2) double vision that worsens when looking to the left (L); and (3) head tilt to the right (R). The mnemonic is R, L, R (the marching rule—conversely, the rule for left superior oblique paralysis is L, R, L). This rule and the lack of ptosis and/or mydriasis differentiate the exotropia of CN IV palsy from that of CN III.


image id=”u0300″/>The abducens supplies the lateral rectus. Hence, its damage prevents eye abduction to the side of the lesion. This results in double vision on horizontal gaze only (horizontal homonymous diplopia). It is often injured in patients with increased intracranial pressure.





















57 Who was Bell?


Sir Charles Bell (1774–1842) was a Scottish neurophysiologist and surgeon. He was not the same Dr. Bell who taught medicine in Edinburgh and made a big impression on young Conan Doyle (thus becoming the accidental model for Sherlock Holmes). That was Joseph Bell, a mesmerizing teacher who even tried his analytical powers on the mystery of Jack the Ripper, the Whitechapel killer of 1888. Charles Bell was instead the soft-spoken son of an Episcopal minister, who after being denied a position in Edinburgh, left for London in 1801. There, he made a name for himself as an artist, thanks to his “Essays on the Anatomy of Painting.” He also attended the military hospital of Haslar, where he had plenty of opportunities to treat the casualties of Wellington’s peninsular campaign. This triggered a lifelong fascination with war, and what it can do to human body and psyche. In 1815, while operating on Waterloo’s wounded, he made sketches and drawings that can still be viewed at the Royal College of Surgeons in Edinburgh. He eventually moved back to his native Scotland, but only after founding the Middlesex Hospital and Medical School. He is remembered not only for his palsy and phenomenon, but also for Bell’s law, which states that the anterior spinal roots carry motor fibers, whereas the posterior carry sensory fibers, including proprioception. He also named the “sense of position” as the “sixth sense”—eventually renamed proprioception by Sherrington.









64 What is the anatomy of CN IX (glossopharyngeal) and CN X (vagus)? How do you test them?


Axons from several brain stem nuclei mingle together to emerge from the neuraxis through two separate nerves, named by early neuroanatomists as glossopharyngeal (IX) and vagal (X) (the vagus was so termed since, as a vagabond, it wanders long distances in the body). In reality, the origin of the two nerves is essentially identical. Function also is similar: motor control of the palate and pharynx (plus, for the IX, sensory supply to the pharynx and posterior third of the tongue). Hence, their clinical testing is not entirely separable. Since the brain stem nuclei of these two nerves receive bilateral innervation from the cortex, their dysfunction results from one of three possibilities: (1) bilateral damage to the cortex or pyramidal tracts (pseudobulbar palsy), (2) brain stem disease (lateral medullary syndrome), or (3) peripheral nerve lesions (jugular foramen syndrome). You can test IX and X by asking patients to say “ahhh” or “ehhh” (see Chapter 6, questions 53 and 54) while observing whether the velum of the palate rises symmetrically. Alternatively, you can use the gag and palatal reflexes. The latter is elicited by touching the patient’s palate with a cotton swab, which causes elevation of the soft palate and ipsilateral deviation of the uvula. The gag is instead triggered by touching the posterior wall of the pharynx (or alternatively, the tonsillar area or base of the tongue). It causes tongue retraction and elevation/constriction of the pharyngeal musculature. In unilateral CN IX and X paralysis, these reflexes result in deviation of the uvula toward the normal side. Lesions of the IX also will result in loss of taste in the posterior third of the tongue, and loss of pain and touch sensations in the same area plus the soft palate and pharyngeal walls. Conversely, unilateral paralysis of CN X’s recurrent laryngeal nerve will cause hoarseness. Bilateral paralysis will cause stridor (requiring tracheostomy).


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Apr 3, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on The Neurologic System

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