Pathophysiology of the Carpal Tunnel Syndrome

Abstract

Carpal tunnel syndrome (CTS) is the most common peripheral nerve disorder. Despite its frequency, the exact pathophysiology remains elusive. It is, however, commonly accepted that CTS affects the large nerve fibres, induces non-inflammatory changes and is driven by mechanisms that remain localised to the lesion site. Clinical diagnosis therefore largely relies on local tests for the large fibre domain such as standard electrodiagnostics, vibrometry or von Frey hair testing within the median nerve territory.

In this review, the current beliefs and resulting clinical guidelines are challenged by summarising novel evidence which suggests the presence of hitherto unrecognised pathophysiological mechanisms. A focus is thereby placed on the contribution of small fibre degeneration, the presence of intraneural inflammation and remote mechanisms to the pathophysiology of CTS. Since these mechanisms seem to be pertinent to CTS, potential approaches to integrate them in the diagnostic work-up of patients with suspected CTS are suggested.

Future work is, however, required to establish their diagnostic validity as well as impact on management and prognosis of patients with CTS.

Zusammenfassung

Das Karpaltunnelsyndrom (KTS) ist die am häufigsten auftretende periphere Nervenstörung. Trotz seiner Häufigkeit bleibt die exakte Pathophysiologie unklar. Dennoch wird allgemein akzeptiert, dass KTS die großen Nervenfasern angreift, nicht entzündliche Veränderungen hervorruft und lokalisierte Mechanismen an der Läsionsstelle auslöst. Daher beruht die klinische Diagnose weitgehend auf lokalen Tests für die großen Fasern, wie z.B. Elektrodiagnostik, Vibrometrie oder von-Frey-Haartest im Innervationsgebiet des N. medianus. Dieser Review stellt die derzeitigen Überzeugungen und die daraus resultierenden klinischen Leitlinien infrage, indem er die neue Evidenz zusammenfasst, die das Vorhandensein von bisher unerkannten pathophysiologischen Mechanismen nahelegt. Dabei liegt der Schwerpunkt auf zur Pathophysiologie des Karpaltunnelsyndroms beitragenden degenerierten kleinen Nervenfasern, intraneuraler Entzündung und Mechanismen abseits der Läsionsstelle. Da diese Mechanismen das Karpaltunnelsyndrom zu beeinflussen scheinen, werden mögliche Ansätze empfohlen, die diese Mechanismen in die Diagnosestellung mit einbeziehen. Um ihre diagnostische Validität ebenso wie ihren Einfluss auf die Behandlung und die Prognose für Patienten mit KTS nachzuweisen, ist jedoch weiterführende Forschung nötig.

Schlüsselwörter

Karpaltunnelsyndrom - Entrapment-Neuropathie - Pathophysiologie - kleine Nervenfasern - Demyelinisierung - Entzündung - Diagnose

Key words

carpal tunnel syndrome - entrapment neuropathy - pathophysiology - small nerve fibres - demyelination - inflammation - diagnosis

¹ Annina Schmid is funded by a Neil Hamilton Fairley Fellowship by the National Health and Medical Research Council (NHMRC) Australia.

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