COMPRESSIVE NEUROPATHIES PN5 (1) Compressive Neuropathies (s. Entrapment Neuropathies, Tunnel Syndromes) Last updated: August 8, 2020 ETIOLOGY .............................................................................................................................................. 1 PATHOPHYSIOLOGY ............................................................................................................................... 1 Double Crush Syndrome ....................................................................................................... 1 CLINICAL FEATURES .............................................................................................................................. 2 DIAGNOSIS ............................................................................................................................................. 2 TREATMENT ........................................................................................................................................... 2 N. MEDIANUS ........................................................................................................................................... 2 Places of compression ........................................................................................................... 2 CARPAL TUNNEL SYNDROME (CTS) ....................................................................................................... 3 PRECIPITATING FACTORS ....................................................................................................................... 3 CLINICAL FEATURES .............................................................................................................................. 3 DIAGNOSIS ............................................................................................................................................. 5 TREATMENT ........................................................................................................................................... 5 Surgery ............................................................................................................................................. 6 N. ULNARIS .............................................................................................................................................. 6 N. ULNARIS AT ELBOW .......................................................................................................................... 6 Clinical Features ............................................................................................................................... 7 Diagnosis .......................................................................................................................................... 7 Treatment ......................................................................................................................................... 7 N. ULNARIS AT WRIST ............................................................................................................................ 8 Treatment ......................................................................................................................................... 9 N. RADIALIS ............................................................................................................................................. 9 CLINICAL FEATURES .............................................................................................................................. 9 DIAGNOSIS ............................................................................................................................................. 9 TREATMENT ........................................................................................................................................... 9 THORACIC OUTLET SYNDROME (TOS) ................................................................................................ 10 CLASSIFICATION & CAUSES ................................................................................................................. 10 Vascular TOS ...................................................................................................................... 10 Neurogenic TOS .................................................................................................................. 10 CLINICAL FEATURES ............................................................................................................................ 10 Neurogenic TOS .................................................................................................................. 10 Vascular TOS ...................................................................................................................... 11 DIAGNOSIS ........................................................................................................................................... 11 Neurogenic TOS .................................................................................................................. 11 Vascular TOS ...................................................................................................................... 12 TREATMENT ......................................................................................................................................... 12 Neurogenic TOS .................................................................................................................. 12 N. SUPRASCAPULARIS ............................................................................................................................ 14 N. ISCHIADICUS ...................................................................................................................................... 14 N. PERONEUS ......................................................................................................................................... 15 Conservative therapy ........................................................................................................... 15 Surgery ................................................................................................................................ 15 N. TIBIALIS POSTERIOR ......................................................................................................................... 15 Treatment ............................................................................................................................. 16 MERALGIA PARESTHETICA .................................................................................................................... 17 MORTON'S NEUROMA ............................................................................................................................ 18 OTHER NERVES ...................................................................................................................................... 18 Pressure-induced injury to segment of peripheral nerve secondary to anatomic / pathologic structures account for 10-20% of all neurosurgery cases! Most frequent: 1. Carpal tunnel syndrome 2. Ulnar nerve compression at elbow. ETIOLOGY 1. Violent muscular activity, forcible joint overextension, prolonged cramped postures (e.g. in gardening). 2. Repeated small traumas (e.g. tight gripping of small tools, excessive vibration from air hammers). 3. Extrinsic compressions - casts, crutches. 4. Intrinsic compressions - tumors, bony hyperostosis, inflammatory edema of adjacent structures, infiltrating substances (e.g. amyloid, hypothyroidism, mucopolysaccharidosis, acromegaly). patients with any polyneuropathy are more vulnerable to mechanical injury of nerves!!! patients with congenital narrowing of osseous tunnel or thickening of overlying retinaculum have predilection. PATHOPHYSIOLOGY usually affects: a) superficial nerves (ulnar, radial, peroneal) at bony prominences (e.g. during sleep or anesthesia) in thin-cachectic persons (esp. alcoholics). b) nerves at narrow osseoligamentous canals (e.g. carpal tunnel). in all cases, at least one side of compressive surfaces is mobile – allows chronic injury: either repetitive “slapping” insult or “rubbing/sliding” against sharp, tight edges with motion at adjacent joint - this explains beneficial effect of splinting. chronic blunt injury / pressure (above perfusion pressure) to nerve → disruption of blood-nerve barrier → microvascular (ischemic) changes, edema → dislocation of nodes of Ranvier → focal segmental demyelination (still reversible with treatment) → axonal disruption, epineurial fibrosis (constant feature!) ISCHEMIA + EDEMA Pressure Result 30 mm Hg impaired axonal transport 40 mm Hg paresthesias and neurophysiologic changes 50 mm Hg axonal block 60 mm Hg complete intraneural ischemia (sensory and motor block) recovery: a) complete - reflects remyelination. b) incomplete - due to Wallerian degeneration and permanent fibrotic changes. nerve compression affects myelinated fibers first (A type > B type > C type) - nerve conduction studies & EMG are usually diagnostic. N.B. larger fibers are more susceptible than small fibers DOUBLE CRUSH SYNDROME COMPRESSIVE NEUROPATHIES PN5 (2) - coexistence of compressive lesions in series along course of peripheral nerve, with one lesion rendering nerve susceptible to distal or proximal compression. first postulated by Upton and McComas in 1973. mechanism: impaired axonal flow, ischemia, and altered nerve elasticity, which lessen the nerve's resiliency. Intrinsic neuropathies additionally affect nerve's susceptibility