MONOGRAPH #34: POLYNEUROPATHY: CLASSIFICATION BY NERVE CONDUCTION STUDIES AND ELECTROMYOGRAPHY Peter D. Donofrio, MD James W. Albers, MD, PhD Approved and reviewed by the AANEM Education committee. Original approval, September 5, 1989. Reviewed and no revisions recommended, September 1994 and October 1998. Education Committee William J. Litchy, MD, Chair Richard D. Ball, MD, PhD William W. Campbell, Jr., MD James M. Gilchrist, MD John J. Halperin, MD Gerald J. Herbison, MD Susan L. Hubbell, MD John C. Kincaid, MD James J. Rechtien, DO, PhD Lawrence R. Robinson, MD Copyright© October 1990 American Association of Neuromuscular & Electrodiagnostic Medicine 2621 Superior Dr NW Rochester, MN 55901 The ideas and opinions contained in this publication are solely those of the authors and do not necessarily represent those of the AANEM. AAEM MlNlMONOGRAPH #34 Electrodiagnostic evaluation of patients with suspected polyneuropathy is useful for detecting and documenting peripheral abnormalities, identifying the predominant pathophysiology, and determining the prognosis for certain disorders. The electrodiagnostic classification of polyneuropathy is associ- ated with morphologic correlates and is based upon determining involve- ment of sensory and motor fibers and distinguishing between predomi- nantly axon loss and demyelinating lesions. Accurate electrodiagnostic classification leads to a more focused and expedient identification of the eti- ology of polyneuropathy in clinical situations. Key words: polyneuropathy electrodiagnosis nerve conduction studies electromyography MUSCLE & NERVE 13~889-903 1990 AAEM MINIMONOGRAPH #34: POLYNEUROPATHY: CLASSIFICATION BY NERVE CONDUCTION STUDIES AND ELECTROMYOGRAPHY PETER D. OONOFRIO, MD, and JAMES W. ALBERS, MD, PhD The electromyographer plays an important role more, the electromyographer can readily identify in the evaluation of patients with established or other primary or superimposed disorders, such as suspected polyneuropathy; no longer is it suffi- polyradiculopathy, that may be clinically indistin- cient to simply confirm the presence or absence of guishable from polyneuropathy . When used as an polyneuropathy. Given the results of conventional extension of the clinical neurologic examination, a electrodiagnostic studies, the electromyographer focused list of specific etiologies consistent with can identify the predominant pathophysiology the combined clinical and electrodiagnostic find- (axonal loss, uniform or segmental demyelina- ings can be developed, useful in directing the sub- tion), establish whether sensory or motor findings sequent laboratory examination. Accuracy in es- predominate, and often determine the temporal tablishing a specific etiology or diagnosis is profile (acute, chronic, old, and/or ongoing) of a related, in part, to appropriate application of elec- peripheral disorder. In addition, the studies pro- trodiagnostic techniques. These include conven- vide a quantitative index of severity that is inde- tional motor and sensory conduction studies, late pendent of the individual patient’s recollection or responses (F response and H reflex), blink re- cooperation. Even in clinically evident polyneuro- flexes, sympathetic skin potentials, and needle pathy, the prognosis often can be established on electromyography . The following summarizes one the basis of electrodiagnostic findings. Further- approach that can be used in examining such pa- tients. From the Department of Neurology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27103 (Dr. Donof- PERIPHERAL NERVE DISORDERS rio) and the Departments of Neurology and Physical Medicine and Reha- bilitation, University of Michigan Medical Center, Ann Arbor, Michigan Initial classifications of nerve disorders were based 48109. upon anatomic and clinical observations following Acknowledgment: The author gratefully acknowledges that portions of focal nerve damage. Waller demonstrated the pre- the unreferenced clinical information were modified with permission from material prepared by D.D. Duane: Classification of neuropathy, in Neurol- dictable degeneration of nerve fibers in the distal ogy Fellows Handout. Rochester, Minnesota, Mayo Clinic Department of stump of a transected nerve, describing the initial Neurology (unpublished, 1972). discontinuities of axolemma with subsequent dis- Address reprint requests to AAEM. 21 Second Street S.W., Suite 306, Rochester, MN 559 solution of ax on^.**^ “Axonotmesis” was used to describe focal destruction of axons and myelin Accepted for publication December 29, 1989 sheaths without interruption of the nerve stroma. CCC 0148-639)(/90/0100889-015 $04.00 Axonal (wallerian) degeneration occurred distal to 0 1990 Peter D. Donofrio, MD, and James W. Albers. MD, PhD. Pub- lished by John Wiley & Sons, Inc. the lesion, identical to the degeneration associated AAEM Minimonograph #34: Polyneuropathy MUSCLE & NERVE October 1990 889 with nerve transection. Recovery was prolonged, and motor conduction velocities and distal laten- occurring first in muscles closest to the site of’ cies remain essentially normal with only minimal damage, and related to regeneration of the axon abnormalities at a time when amplitude is substan- via intact endoneurial tubes. “Neurapraxia” was tially diminished. Insertional and rest abnormali- used to define a motor paralysis not associated ties on needle electromyography can be apparent with axonal degeneration; recovery occurred within 7 to 10 days, although may not be evident within hours to months. for up to 3 weeks depending upon the proximity Histopathologic evaluation of experimental of the denervated muscle to the site of nerve sec- nerve compression has increased our understand- tion. Initial abnormality consists of prolonged in- ing of “neurapra~ia.~~~’~~Defects have been dem- sertional activity, followed by the appearance of onstrated under the edges of the compressing sustained positive waves, spontaneous fibrillation tourniquet without extension throughout the com- potentials, and complex repetitive discharges. pressed area. Invagination of one myelin segment With incomplete axon loss lesions, reduced re- into the next has been associated with conduction cruitment is recorded rather than complete ab- block by occluding the node of Ranvier, resulting sence of voluntary MUAPs. MUAPs initially are of in ionic current b10ckade.l’~ normal amplitude, duration, and configuration. A Electrodiagnostic evaluation of polyneuropathy slight increase in the percentage of polyphasic is similar to the evaluation of focal nerve lesions. MUAPs may appear after 10 to 14 days, presum- It is necessary to determine the presence of sen- ably secondary to sprouting or collateral regenera- sory and motor fiber involvement and to accu- tion of surviving motor ax on^.^^^ Within months. rately distinguish between axon loss and demyelin- MUAPs are of increased amplitude and duration ating lesions. Clearly, many polyneuropathies are with an increased percentage of polyphasic poten- neither purely axonal or demyelinating, but tials. rather a combination of both with predominance In contrast, different electrodiagnostic results of one or the other. The results of conventional are obtained following either focal or diffuse electroneuromyography usually can make this demyelination. ’” With a complete focal conduc- distinction. tion block, initial findings are identical to those de- scribed for nerve transection. Motor and sensory PHYSIOLOGIC BASIS OF ELECTRODIAQNOSTIC evoked responses cannot be demonstrated with ABNORMALITIES nerve stimulation proximal to the lesion; however, The characteristic electrodiagnostic findings in stimulation distal to the lesion results in normal purely axon loss lesions are best demonstrated fol- responses. Regardless of the duration of the phys- lowing total axonal interruption as in nerve iologic block, all nerve conduction studies distal to transection. Attention to the sequential abnormal- the lesion remain normal. Insertional and resting ities is useful in identifying those components of abnormalities may not develop on needle exami- the electrodiagnostic examination most sensitive to nation. If present, those abnormalities are modest, axonal disorders. Landau demonstrated that mus- commensurate with the mild degree of axon loss cle contraction could be evoked for several days often resulting from insults severe enough to pro- with stimulation of a transected nerve; the re- duce conduction block. sponse then diminished with complete loss of ex- The electrodiagnostic abnormalities associated citability after 4 to 5 days.’43 with focal demyelination without conduction block Clinical electrodiagnostic evaluation demon- are similar to those seen in chronic nerve com- strates similar findingsY3 Immediately after pression, ie, substantial reduction of conduction transection, motor and sensory evoked response velocity across the lesion. 159 amplitude, conduction velocity, and distal latency In uniform demyelinating disorders, the remain normal with stimulation distal to the le- marked reduction of conduction velocity is dispro- sion. Needle electromyography demonstrates nor- portionate to the relatively normal evoked re- mal insertional and rest activity, although volun- sponse amplitude with distal ~timulation.~~There tary motor unit action potentials (MUAPs) cannot is relatively homogeneous involvement of all my- be activated. Within days, a progressive decrease elinated fibers. in compound muscle action potential (CMAP) and