66

5Topical Diagnosis and Differential Diagnosis of Neurological Syndromes

Fundamentals . . .	66		Sensory Disturbances . . .	72
Muscle Weakness and Other			Disturbances of Consciousness . . .		76
Motor Disturbances . . .		66	Dysfunction of Specific Areas of the Brain . . .			77

Fundamentals

The neurological deficits produced by a lesion in any given area of the nervous system are characteristic of the area involved and relatively independent of the type of lesion. Thus, the clinical manifestations of neurological disease are determined above all by the site of the lesion. A thorough knowledge of these relationships is essential in clinical practice. The first step in diagnostic assessment is always the localization of the disease process in the nervous system. This can usually be done with great precision based on the information obtained in the clinical interview and neurological examination. The etiology is then sought in a second step with the aid of further information (course of the disease over time, any accompanying nonneurological manifestations, results of ancillary tests).

In this chapter, we will show how the clinical manifestations of neurological disease can be used to make inferences about the site of the lesion and its possible etiologies. We will first describe the typical findings of lesions affecting individual functional systems (the motor and somatosensory systems) and then those of lesions in particular areas of the brain. The manifestations of diseases affecting the spinal cord and peripheral nerves will be discussed in the relevant, later chapters.

Muscle Weakness and Other Motor Disturbances

Anatomical Substrate of

Motor Function

It is a useful simplification to consider the motor system as consisting of the following components (Fig. 5.1):

First (central) motor neuron (neurons in the precentral gyrus). The axons travel in the corticobulbar and corticospinal tracts through the internal capsule and cerebral peduncle and terminate either in the cranial nerve nuclei of the pons and medulla (corticobulbar pathway) or on the anterior horn cells of the spinal cord (pyramidal pathway). Lesions of the first motor neuron in the precentral gyrus, or at any other site, produce the following deficits:

spastic weakness (elevated muscle tone, diminished raw strength, and impaired fine motor control);

increased intrinsic muscle reflexes, spreading of reflex zones, and pathological reflexes (Babinski, Oppenheim, and Gordon, pathologically brisk Hoffmann sign and Trömner reflex, inextinguishable or asymmetrically persistent clonus); diminished or absent extrinsic muscle reflexes (e. g., abdominal skin reflex);

no muscle atrophy (though there may be mild atrophy of disuse in the later course of disease);

asymmetry of the reflexes if the lesion is unilateral.

The second (peripheral) motor neuron originates in one of the motor relay stations mentioned above (the motor cranial nerve nuclei or the anterior horn cells of the spinal cord). It consists of a cell body (ganglion cell) and an axon that travels by way of a spinal nerve root, plexus, and peripheral nerve to the skeletal muscle. Each ganglion cell, together with its axon and the muscle fibers that it innervates (there may be many, or only a few), comprises a single motor unit. The following deficits are associated with a lesion of the peripheral motor neuron:

flaccid weakness (diminished muscle tone and raw strength);

diminished or absent intrinsic muscle reflexes;

muscle atrophy becoming evident about three weeks after injury and progressing thereafter.

Motor end plate and muscle. In addition to the first and second motor neurons, normal motor function requires effective impulse transmission from the peripheral nerve to the muscle fiber, followed by fiber contraction. A lesion or functional disturbance of either or both of these elements causes flaccid weakness usually accompanied by atrophy and diminished reflexes (p. 275).

Because every movement, as we have seen, is the product of a complex interaction of many different ana-

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Muscle Weakness and Other Motor Disturbances 67

Fig. 5.1 Anatomical substrate of movement (modified from Liebsch, R.: Intensivkurs Neurologie. Urban & Schwarzenberg, Munich, 1996, and Mumenthaler, M.:

Neurologische Differenzialdiagnose, 4th edn, Thieme, Stuttgart, 1992).

	5
pontine nuclei	Differential Diagnosis
	Topical Diagnosis and

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68 5 Topical Diagnosis and Differential Diagnosis of Neurologic Syndromes

tomical structures, motor processes are subject to a wide range of pathological disturbances. Typical findings of lesions of individual components of the motor system are listed in Table 5.1. The following table, in contrast, begins with certain typical constellations of

motor deficits, then lists the likely site(s) of the lesion producing each, and finally some of the possible etiologies. Table 5.2 thus reflects the “classic” threefold paradigm of clinical thinking, from the physical findings to the site of the lesion to the diagnosis.

Table 5.1 Aspects of motor function and their localizing significance

Criterion	Motor neuron in	Spinal nerve root or	Central motor path-	Extrapy-	Cerebellum
	anterior horn	peripheral nerve	way (corticobulbar	ramidal
			and corticospinal)	system
Raw strength				normal	normal
Tone				possibly rigid,
				possibly
Muscle atrophy	++	++	(except for possible
			atrophy of disuse)
Intrinsic muscle reflexes	or absent	or absent		normal	normal
Extrinsic muscle reflexes	or absent	or absent		normal
Pyramidal tract signs			+
Coordination				normal or
Distribution of weakness	no rule	corresponding to the	global	no weakness	no weakness
		affected root or nerve
Fasciculations	++	rare

Table 5.2 Patterns of distribution of weakness and their localizing significance

Pattern of distribution of weakness	Type of paralysis	Anatomical substrate	Causative illnesses; remarks
Focal, isolated, usually asym-	flaccid	peripheral nerve	when a purely motor nerve is involved,
metrical weakness of individual		lesion		usually high-grade paresis of the muscle(s)
muscles or muscle groups				that it innervates; when a mixed nerve is
				involved, there are additional sensory and/or
	flaccid	nerve root lesion		autonomic deficits
				paresis and reflex deficits (if any) in the
				segmentally innervated muscle(s), usually
				accompanied by a sensory deficit in the
	flaccid	loss of anterior horn		dermatome of the affected nerve root
				initial stage of spinal muscular atrophy;
		ganglion cells		fasciculations are usually seen in the muscles
	flaccid	muscle ischemia		innervated by the lost anterior horn cells
				compartment syndromes, e. g., tibialis ante-
				rior syndrome; sensation intact, muscle
				contracted
Symmetrical, mainly proximal	flaccid	myopathy	initial stage of limb girdle muscular dystro-
weakness	flaccid	loss of anterior horn		phies
				initial stage of certain types of spinal
		ganglion cells		muscular atrophy
Symmetrical, mainly distal	flaccid	myopathy	initial stage of certain types of muscular
weakness				dystrophy or myotonia, e. g., Steinert
				myotonic dystrophy (in such cases usually
				beginning distally, and involving mainly
	flaccid	lesion of distal		extensor muscles)
				polyneuropathy; often accompanied by
		portion of multiple		paresthesiae and sensory deficits
		peripheral nerves

Continued

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Muscle Weakness and Other Motor Disturbances 69

Table 5.2 Patterns of distribution of weakness and their localizing significance (continued)

Pattern of distribution of weakness	Type of paralysis	Anatomical substrate		Causative illnesses; remarks
Hemiparesis:	spastic	lesion of the		ischemic stroke, intracerebral hemorrhage,
hemiparesis including the face
			contralateral motor		tumor, trauma, infection, or inflammation;
			cortex or cortico-		the weakness is usually mainly distal (the
			bulbar and cortico-		ends of the limbs, esp. the hands, have a
			spinal pathways as		larger cortical representation) and accom-
			they pass through the		panied by impairment of fine motor control
			corona radiata and		and sensation
			internal capsule,
			down to the level of
hemiparesis sparing the face	spastic		the cerebral peduncle	focal lesion, usually microinfarct
			lesion of the
(no weakness of the muscles of			contralateral caudal		(contralateral hemiparesis usually accom-
facial expression)			portion of the brain-		panied by sensory deficits and caudal cranial
	spastic		stem		nerve deficits, see below)
			hemisection of the		e. g., trauma or compression by a tumor;
			spinal cord at a high		may be accompanied by ipsilateral
			cervical level, on the		hypesthesia and contralateral (dissociated)
			side of the paretic		deficit of pain and temperature sensation
			limbs		below the level of the lesion, as well as
					segmentally delimited flaccid paresis at the
					level of the lesion (because of anterior horn
	spastic	brainstem lesion			cell involvement)
Special form: crossed unilateral					combination of ipsilateral cranial nerve deficit
weakness (face on one side, body			(medulla, pons, or		and contralateral hemiparesis; if the affected
on other side)			midbrain)		cranial nerve is a motor nerve, there may be
					flaccid weakness in the muscles it innervates
Quadriparesis/global weakness:	spastic	lesion of the cerebral		e. g., hypoxic brain injury after cardiorespira-
			cortex of both hemi-		tory arrest
	spastic		spheres	e. g., multiple sclerosis
			lesion of the deep
			cerebral white matter
	spastic		of both hemispheres	e. g., locked-in syndrome
			(partial) transverse
			lesion of the brain-
			stem interrupting all
			corticospinal projec-
	spastic		tions	e. g., trauma or compression by tumor;
			high cervical spinal
			cord transection		accompanied by sensory deficit in all modali-
					ties below the level of the lesion (sensory
					level) and segmentally delimited flaccid
	mixed spastic/	loss of central motor			weakness at the level of the lesion
					amyotrophic lateral sclerosis
	flaccid		neurons and anterior
	flaccid		horn ganglion cells	acute anterior poliomyelitis, advanced stage
			loss of anterior horn
			ganglion cells at		of spinal muscular atrophy
			many different spinal
	flaccid		cord levels	e. g., advanced stage of Guillain−Barré
			lesion of multiple
			nerve roots at		syndrome (acute or chronic recurrent)
			multiple segmental
	flaccid		levels	advanced stage of various types of muscular
			myopathy
					dystrophy, generalized form of myasthenia;
		disease of an internal			myositis
	usually no objec-				e. g., thyroid dysfunction
	tive evidence of		organ
	weakness		psychogenic
			depression

Continued

5

Topical Diagnosis and Differential Diagnosis

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70	5 Topical Diagnosis and Differential Diagnosis of Neurologic Syndromes
		Table 5.2 Patterns of distribution of weakness and their localizing significance (continued)
		Pattern of distribution of weakness	Type of paralysis	Anatomical substrate		Causative illnesses; remarks
		Paraparesis	spastic	bilateral parasagittal		often in falx meningioma; sometimes accom-
					lesion (cortical repre-		panied by sensory deficits in the lower limbs
					sentation of the		due to simultaneous involvement of the post-
					lower limbs in the		central gyri; there may also be neuropsycho-
			spastic		precentral gyri)		logical abnormalities and urinary dysfunction
					thoracic spinal cord		e. g., trauma or compression by tumor;
					transection		sensory level, possible segmentally delimited
			spastic	disease process			weakness at the level of the lesion
							spastic spinal paralysis; purely motor deficit
					affecting the corti-		(no sensory deficit)
					cospinal tracts bilater-
			flaccid		ally	initial stage of Guillain−Barré syndrome
					acute lesion of
					multiple lumbar		(often with ascending weakness); cauda
					nerve roots		equina syndrome due to massive lumbar
			flaccid	lesion of multiple			intervertebral disk herniation
							polyneuropathy; usually in combination with
					peripheral nerves of		sensory deficits and reflex deficits (e. g.,
			flaccid		the lower limbs		Achilles’ reflex)
					myopathy		e. g., initial stage of myotonic dystrophy

Motor Regulatory Systems

The smooth, precise, and economical execution of a movement requires a properly functioning “regulatory system” in addition to the effector components discussed above. The regulatory system must do the following:

integrate proprioceptive input from the peripheral nerves, posterior columns (fasciculus gracilis and fasciculus cuneatus), thalamus, and thalamocortical pathways, along with further input from the vestibular apparatus and the visual system, and use this “feedback” data to optimize each phase of the movement at every moment;

plan the force and amplitude of the movement (extrapyramidal system and cerebellum);

coordinate the activity of all of the muscles taking part in a movement and, in particular, ensure the effective complementary functioning of agonist and antagonist muscles (extrapyramidal system, cerebellum, and spinal cord).

A loss of function of one or more components of this regulatory system impairs the execution and coordination of movement. Disturbances of this type are typically manifest as:

ataxia,

hypokinesia,

involuntary movements.

Ataxia is an impairment of the smooth performance of goal-directed movement (repeated deviation from the ideal line of a movement). The different types of ataxia have specific clinical features, depending on the nature and location of the underlying lesion:

Cerebellar ataxia is characterized by irregularity of the entire course of a movement. A lesion in a cerebellar hemisphere produces ataxia in the ipsilateral limbs, while a vermian lesion mainly produces truncal ataxia

(ataxia of stance and/or gait). On the other hand, involvement of the dentate nucleus or its efferent fibers causes intention tremor: in targeted movements, the deviation from the ideal line of approach increases as the limb approaches the target (Fig. 3.20, p. 29).

Central sensory ataxia results from impaired position sense due to lesions of the somatosensory cortex, the thalamus, or the thalamocortical pathways.

Posterior column ataxia is produced by lesions of the afferent somatosensory pathways in the dorsal portion of the spinal cord (fasciculus gracilis and fasciculus cunea- tus—also known as the columns of Goll and Burdach). It is most apparent when the patient walks; it is regularly accompanied by impaired proprioception and position sense. Patients can compensate for posterior column ataxia to some extent with visual cues; this form of ataxia is thus appreciably worse in the dark, or when the patient’s eyes are closed, than in a well-lit room with the patient’s eyes open.

!The distinguishing characteristic of spinal, as opposed to cerebellar, ataxia is that it is mainly evident when visual input is removed.

Peripheral sensory ataxia is caused by disease processes affecting the peripheral sensory nerves, e. g., polyneuropathy, and is associated with loss of reflexes and impaired epicritic sensation.

Other types of ataxia. Frontal lobe lesions sometimes cause contralateral ataxia; motor weakness can also impair motor coordination, causing ataxia. Psychogenic ataxia is typified by its irregularity and by the lack of constant, objectifiable neurological deficits. Patients with psychogenic ataxia do not fall.

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Muscle Weakness and Other Motor Disturbances

Hypokinesia is generalized slowing of all types of movement.

It is typically found in (hypokinetic) Parkinson disease (p. 128). Spontaneous movements are sparse or absent, automatic accessory movements cease (e. g., arm movements during walking), and all voluntary movements are slowed. The muscles are rigid and the cogwheel phenomenon is usually demonstrable (p. 30).

It is also found in depression as a sign of generally diminished drive; in such cases, it is not accompanied by any other neurological deficit.

Involuntary movements come in many varieties, the more important of which are listed in Table 5.3. The phenomenology and localizing significance of each type of involuntary movement are described.

Table 5.3 Involuntary movements and movement disorders

Designation	Manifestations	Localization; Remarks

Spontaneous muscle activity not producing movement

Fibrillations	phasic contractions of individual muscle
	fibers, not visible to the naked eye, only
	demonstrable by EMG
Fasciculations	brief, irregular contractions of individual
	groups of muscle fibers, visible to the
	naked eye
Myokymia	visible waves of contraction passing across
	many different fiber bundles in a muscle or
	group of muscles

due to contractions of individual muscle fibers; pathological at rest or as prolonged insertional activity in the EMG (p. 58)

due to contractions of individual motor units; always pathological; especially typical of chronic lesions affecting the anterior horn ganglion cells

unknown

Hyperkinetic phenomena
Myorrhythmia	rhythmic twitching in a muscle group	central nervous system
	(always the same one) producing move-
	ment; frequency usually 1−3 Hz
Myoclonus	nonrhythmic, rapid, large-amplitude,	cerebral cortex, cerebellum; seen physio-
	sometimes very intense twitching of one	logically in persons who are falling asleep
	or more muscles, producing visible move-	(hypnagogic myoclonus)
	ment
Tremor	rhythmic oscillation (usually fine, some-	central nervous system (mainly cere-
	times coarse), at a frequency that remains	bellum, extrapyramidal system)
	roughly constant for the affected
	individual, of more or less constant locali-
	zation; may be observed at rest (rest
	tremor) or with action (action tremor;
	e. g., postural tremor, kinetic tremor,
	intention tremor)
Chorea	brief and relatively rapid, shooting muscle	basal ganglia/striatum
	contractions, mainly distal, nonrhythmic,
	irregular, of varying localization, some-
	times putting the joints into extreme posi-
	tions for a brief period of time
Athetosis	like chorea, but slower, writhing move-	basal ganglia
	ments with longer-lasting hyperflexion or
	hyperextension of the joints
Ballism	brief, shooting muscle contractions, mainly	subthalamic nucleus
	proximal and therefore causing
	pronounced movement (flinging move-
	ments of the limbs, jactation)
Dystonia	involuntary, longer-lasting muscle contrac-	basal ganglia
	tion that slowly overcomes the resistance
	of the antagonist muscles, usually leading
	to turning movements and bizarre
	postures of individual parts of the body
	(trunk, limbs, head)
Tics and ticlike movements	irregular muscle contraction limited to	psychogenic
	certain parts of the body, rapid, but not
	lightninglike
		Continued

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5

Topical Diagnosis and Differential Diagnosis