Keywords Cutaneous Silent Period - Neurology - Neurophysiology
INTRODUCTION
In 1922, German physiologist Paul Hoffmann described the basis for a neurophysiological
test that enables the assessment of the integrity of the structures of the spinal
cord and of the A-delta small sensory fibers. His monograph Untersuchungen über die eigenreflexe (sehnenreflexe) menschlicher muskeln (“Investigations into the self-reflexes [tendon reflexes] of human muscles) was published
by Springer in 1922.[1 ]
Best remembered for the description of the H reflex, a monosynaptic reflex pathway
whereby stimulated afferent, sensory nerves synapse with anterior horn cells within
the spinal cord and subsequently activate muscle fibers innervated by these motor
units,[2 ] or by the sign that bears his name, described in March 1915, in “Concerning a method
for assessing the success of a nerve suture”.[3 ]
He described the sign used to assess nerve regeneration, which was checked by lightly
percussing with an extended finger in an area located over the proximal nerve stump
or by percussing distally to proximally along the segment of nerve injury or repair.
The sign was considered positive if percussion at these sites caused a tingling phenomenon,
which radiated in the sensory distribution of the peripheral nerve, known as Hoffmann and Tinel sign .[2 ]
[4 ]
With the postulate of a monosynaptic transmission, Hoffmann made a significant contribution
to the elucidation of functional principles in the central nervous system. This also
applies to the interpretation of the postreflective, temporary decrease in the tonic
basic innervation, which he interpreted as the inhibitory reflex of the spinal cord
and which later received great attention under the term silent period , describing exteroceptive suppression, by the effect of muscle contraction during
volitional electromyography (EMG) activity.
THE CUTANEOUS SILENT PERIOD TEST
THE CUTANEOUS SILENT PERIOD TEST
The cutaneous silent period (CSP) is the transient suppression of continuous EMG activity
induced by sensory nerve stimulation. It has been more studied in hand muscles after
electrical stimulation of finger nerves, but other recording sites have been used
as well. Since the sensory stimuli that mediate the CSP are transmitted mainly by
slow-conducting A-delta-type nociceptive fibers that reach the posterior horn of the
medulla (laminae of Rexed I and V) and produce pre- or postsynaptic inhibition, from
motor neurons, transmitted through of interspinal motor neurons, it has been suggested
that the CSP can be considered part of a global detrimental response.[5 ] The functional significance of the CSP may be to prepare the limbs to quickly move
away from an attacking object, preferentially inhibiting the muscles that mediate
reaching and grasping while enabling the activation of the proximal muscles that retract
the limb.[6 ]
It has been proposed that the CSP may be useful in neurophysiological assessment to
investigate spinal nociception, sensorimotor integration, and motor control. Since
the CSP has been found to be impaired in several disorders of motor control, it seems
conceivable that the interneuronal substrate mediating CSP represents the final common
pathway subservient to several aspects of motor control.[6 ]
The clinical usefulness of the CSP depends on the possibility of evaluating proximal
segments and components of sensory nerves that are not assessed by conventional neuroconduction
studies. In a comprehensive review divided in two parts, Kofler et al.[7 ]
[8 ] (2019), examining the literature from the last 25 years on pathophysiological conditions,
reported that the CSP may have a diagnostic role in the evaluation of small-fiber
neuropathies, in particular axonal polyneuropathies that affect purely or predominantly
fibers with small diameters. Furthermore, in central nervous system diseases, the
most useful clinical application of the CSP appears to be the functional diagnosis
of intramedullary lesions, such as tumors, and myelopathy.[7 ]
[8 ]
We agree with Serrao[9 ] (2019) that the CSP is a potentially underused tool in clinical neurophysiology.[9 ] The CSP has been found to be abnormal in several other diseases involving the peripheral
and central nervous systems. However, as Kofler et al.[7 ]
[8 ] state, small population samples and lack of test-retest reliability represent limitations
that will need to be addressed in future studies.
PAUL HOFFMANN
Paul Hoffmann was born on July 1st, 1884, in Dorpat, Russia (currently called Tartu,
and located in Estonia). His father Friedrich was a professor of internal medicine
in Dorpat.[2 ]
He studied medicine in Berlin and Leipzig, where he received his doctorate in 1909.
After 2 years as an employee of the Berlin University, he became an assistant at the
Physiological Institute of the University of Würzburg in 1911 and completed his habilitation
there in 1912 under Maximilian von Frey.
As early as 1912, Paul Hoffmann received his habilitation with his thesis on “The
flow of action of the muscle poisoned with Veratrin”. The most fruitful time of his
scientific life were the years from 1909 to 1922 in Berlin and Würzburg.
In 1910, Paul Hoffmann published the fundamental work on muscle reflexes as “Contributions
to the knowledge of human reflexes with special consideration of electrical phenomena”.
In it, he described the direct and the reflex response in the triceps surae muscle
in humans after electrical stimulation of the tibial nerve in the popliteal fossa.
Paul Hoffmann was appointed Professor of Physiology at the Freiburg Faculty of Medicine
in 1924, where he succeeded Johannes von Kries, the well-known sensory physiologist.
He came to Freiburg as a relatively young professor, where he met many well-known
scientists, some of whom later received the Nobel Prize, such as Wieland in 1927 for
chemistry, and Spemann in 1935 for medicine and physiology. Paul Hoffmann remained
in Freiburg until his retirement in 1955, dying in 1962 of a heart attack.[2 ]
In conclusion, in 1950, J.W. Magladery, from Baltimore, in 1950 named H-Reflex in
honor of Paul Hoffmann.[2 ] He has received an honorary chair from the Universidade de Santiago de Compostela,
in Spain, and an honorary doctorate from the universities of Zurich and Berlin, as
well as the Hereditary Medal of the German Neurological Society.[2 ] Some authors have described him as the “originator” of modern neurophysiology in
Germany.
Despite the limited amount of articles, we agree with Kofler et al.,[7 ]
[8 ] who showed that the potential clinical usefulness of the CSP depends on the possibility
of evaluating segments and components of sensory nerves that are not exhaustively
evaluated by standard electrodiagnostic methods. The CSP may have a diagnostic role
in the evaluation of small-fiber neuropathies, diseases of the central nervous system,
and the functional diagnosis of intramedullary lesions.
Source: Wikipedia.
Figure 1 Paul Hoffmann.
Bibliographical Record
