72 5 Topical Diagnosis and Differential Diagnosis of Neurologic Syndromes

Table 5.3 Involuntary movements and movement disorders (continued)

Designation	Manifestations	Localization; Remarks

Other

Spasms	muscle contractions of variable frequency
	and intensity, occurring at irregular inter-
	vals, occasionally painful; two examples are
		hemifacial spasm (Fig. 11.19) and
		blepharospasm
Cramps	long-lasting, tonic contractions of
	individual muscles or muscle groups, fixed
	position of the joints, usually painful, often
	in the calf

facial nerve lesion, extrapyramidal disorder (a type of dystonic movement disorder); very rarely psychogenic

of muscular origin

Sensory Disturbances

Anatomical Substrate of Sensation

It is another useful simplification to consider the somatosensory system as consisting of the following components (Fig. 5.2, Table 5.4):

The peripheral part of the somatosensory system contains sensory (afferent) nerves and receptors that are specialized for the perception of the individual modalities of somatic sensation.

Sensory receptors in the periphery are classified into three principal types. Exteroceptive receptors (exteroceptors) transduce physical stimuli from the external

Table 5.4 The somatosensory system

peripheral	receptors	exteroceptors (mechanoand
portion		thermoreceptors)
		proprioceptors (body posture,
		joint position, tension in muscles
		and tendons)
		nociceptors
	nerve fibers	peripheral nerves, plexuses,
		posterior roots
central	spinal cord	posterior columns
portion		anterolateral columns
		spinocerebellar tracts
	brainstem	posterior column fibers termi-
		nate in synaptic relay stations in
		the medulla (nucleus gracilis,
		nucleus cuneatus); the efferent
		fibers of these nuclei ascend in
		the brainstem as the medial
		lemniscus and terminate in the
		thalamus
		the spinothalamic tracts ascend
		the spinal cord in the antero-
		lateral columns (fasciculi) and
		terminate in the thalamus
		the spinocerebellar tracts termi-
		nate in the cerebellum.
	cerebral	thalamus
	hemispheres	thalamocortical tracts
		somatosensory cortex

environment (e. g., mechanoreceptors, thermoreceptors).

Proprioceptive receptors (proprioceptors) inform the nervous system about head and body posture, the positions of the joints, and tension in muscles and tendons (muscle spindles and Golgi tendon organs). Finally, the nociceptors, which subserve pain, occupy an intermediate position between the exteroand proprioceptors. The density of somatosensory receptors is greatest in the skin, but they are also found in most other tissues of the body, including the viscera (but not in the brain or spinal cord!).

Afferent sensory nerve fibers run in the peripheral nerves, plexuses, and posterior spinal nerve roots. These are the axons of the first somatosensory neurons, whose cell bodies lie in the spinal ganglia (dorsal root ganglia). All other sensory neurons have their cell bodies within the central nervous system.

The central part of the somatosensory system comprises all of the somatosensory pathways and nuclei of the spinal cord, brainstem, and cerebral hemispheres. These can be classified, according to their function, as follows:

Posterior column system. The centripetal processes of the pseudounipolar spinal ganglion cells (first sensory neuron) that subserve epicritic sensation carry information from both exteroceptors (tactile sense, stereognosis and vibration) and proprioceptors (position sense). They travel by way of the posterior columns to the nucleus gracilis and nucleus cuneatus of the medulla, without any intervening relay in the spinal cord. These medullary nuclei contain the second sensory neurons, whose axons, in turn, form the medial lemniscus, which travels onward to the thalamus.

Lesions affecting the posterior column system impair all of the “high-resolution” somatosensory modalities:

diminished ability to recognize objects by touch (astereognosia) and impaired two-point discrimination;

impaired vibration sense (pallhypesthesia or pallanesthesia) and impaired position sense and kinesthesia;

Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme All rights reserved. Usage subject to terms and conditions of license.

	Sensory Disturbances	73
Fig. 5.2	Anatomical substrate
of somatic sensation.
		5
		Topical Diagnosis and Differential Diagnosis

köb

Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme aöbkj ö

All rights reserved. Usage subject to terms and conditions of license.

74 5 Topical Diagnosis and Differential Diagnosis of Neurologic Syndromes

unsteady stance and gait (spinal ataxia, see below) due to the lack of proprioceptive feedback regarding the posture and movements of the head, trunk, and limbs.

Anterolateral column system. The centripetal processes of the pseudounipolar spinal ganglion cells (first sensory neuron) that subserve protopathic sensation (pain, temperature sensation, coarse touch and pressure) form synapses onto second sensory neurons in the posterior horn of the spinal cord. The axons of these cells cross the midline in the anterior spinal commissure and then ascend in the spinal cord and through the brainstem to terminate in the thalamus. Fibers related to pain and temperature sensation travel in the lateral spinothalamic tract, fibers related to coarse touch and pressure in the anterior spinothalamic tract.

Lesions affecting the lateral spinothalamic tract in the spinal cord or brainstem, or the corresponding thalamic nuclei, produce a dissociated sensory deficit: pain and temperature sensation are impaired below the level of the lesion, while touch remains intact. The deficit is contralateral to the lesion because the lateral spinothalamic tract is crossed.

Thalamocortical system. The axons of the second neurons of both the posterior column system and the anterolateral column system terminate in the thalamic nuclei that contain the third neurons of the somatosensory system. These neurons, in turn, send their axons by way

of the posterior limb of the internal capsule to the primary somatosensory cortex (postcentral gyrus) and the neighboring association areas. The third neurons thus belong to the so-called thalamocortical system. Lesions of this system produce a contralateral hemisensory deficit, which usually affects all of the somatosensory modalities, though sometimes to different extents.

The spinocerebellar system conveys information regarding tension and stretch of muscles and tendons from the muscle spindles and Golgi tendon organs to the paleocerebellum. The main spinal pathways used by this system are the posterior spinocerebellar tract (which exclusively carries information from the ipsilateral half of the body) and the anterior spinocerebellar tract (which carries information from both sides of the body). The paleocerebellum, in turn, gives off multiple efferent pathways, which influence muscle tone to ensure the smooth cooperative functioning of agonist and antagonist muscle groups in standing and walking. The paleocerebellum thus plays an important role in the regulation of balance, though its activity is wholly unconscious. Lesions of the spinocerebellar pathways and paleocerebellum cause ataxia of stance and gait (see above).

Table 5.5 is analogous to Table 5.2; it provides an overview of the typical constellations of somatosensory deficits and their pathoanatomical basis. We have not mentioned any specific diagnoses in this table in order to keep it perspicuous. Some of the typical clinical findings are illustrated in Fig. 5.3.

Tabelle 5.5 Patterns of distribution of somatosensory deficits

Pattern of distribution of deficit	Sensory qualities affected	Anatomical substrate; remarks
sharply delimited, unilateral, focal,	all	lesion of the peripheral (sensory) nerve
asymmetrical		trunks; maximal sensory deficit in the auto-
		nomous zone of the affected nerve; hyp-
		esthesia generally more pronounced than
		hypalgesia; concomitant impairment of
		sweating in the area of the deficit

less sharply delimited, unilateral, segmental, asymmetrical

gradually increasing from proximal to distal, bilaterally symmetrical (stocking-and- glove distribution)

segmental, bilaterally symmetrical

all

diminished vibration and position sense at first; the remaining sensory qualities may be lost as the deficit progresses

pain and temperature sense

lesion of the spinal nerve roots; hypalgesia more pronounced than hypesthesia in monoradicular lesions

polyneuropathy; sometimes also seen in polyradiculopathy

lesion of the anterior commissure of the spinal cord, which contains the decussating fibers of the lateral spinothalamic tract; exclusively at a particular segmental level, without damage to ascending pathways

unilateral below a given spinal cord level	pain and temperature sense		lesion of the contralateral lateral
	vibration and position sense			spinothalamic tract
			lesion of the ipsilateral posterior columns
		all qualities other than pain and		lesion of one-half of the spinal cord, regu-
		temperature on the side of the le-		larly producing ipsilateral spastic hemipare-
		sion; pain and temperature con-		sis below the level of the lesion, as well as
		tralaterally		unilateral segmental flaccid paresis at the
				level of the lesion and on the same side as
				the lesion

Continued

Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme

All rights reserved. Usage subject to terms and conditions of license.

Sensory Disturbances	75

Tabelle 5.5 Patterns of distribution of somatosensory deficits (continued)

Pattern of distribution of deficit	Sensory qualities affected	Anatomical substrate; remarks
bilateral below a given spinal cord level	all	lesion of the entire cross-section of the
		spinal cord; regularly accompanied by
		spastic paraparesis below the level of the
		lesion and by bilateral segmental flaccid
		weakness at the level of the lesion
		The sensory deficits of both uniand bilateral
		spinal cord damage are found below the level
		of the most severe anatomical lesion.
unilateral, including the face	all	lesion of the contralateral thalamus, or of
		the ascending thalamocortical projection
		passing through the internal capsule;
	pain and temperature sense	contralateral parietal cortex (rare)
		thalamic lesion on the side opposite the
		sensory deficit; may be accompanied by
		spontaneous pain on the affected side of
		the body, as well as abnormally prolonged
		pain in response to a stimulus that usually
		produces only brief pain (= hyperpathia);
		very rarely due to a cortical lesion
unilateral, sparing the face	all	circumscribed lesion of the contralateral
		dorsal internal capsule, or unilateral high
		cervical cord lesion (see above)

a

b

c

e

5

Topical Diagnosis and Differential Diagnosis

Fig. 5.3 Typical patterns of distribution of somatosensory deficits. a Peripheral nerve lesion: meralgia paraesthetica due to a lesion of the lateral femoral cutaneous n. b Radicular lesion: typical sensory deficit in L5 radiculopathy. c Polyneuropathy: distal, stock-

ing-and-glove sensory deficit. d Central lesion: contralateral hemisensory deficit. e Spinal cord lesion at the T6 level: hemihypesthesia below the level of the lesion.

köb

Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme aöbkj ö

All rights reserved. Usage subject to terms and conditions of license.