Case 18

Case 18





EDX FINDINGS AND INTERPRETATION OF DATA


The abnormal EDX findings in this case include:



2. Multiple partial conduction blocks bilaterally in the forearms. In comparing of responses obtained by distal versus proximal stimulation, the left median compound muscle action potential (CMAP) declined in amplitude from 2.5 mV distally to 1.2 mV proximally (52% amplitude loss), without increase in duration and with an obvious change in waveform morphology (Figure C18-1A). The left ulnar CMAP decreased in amplitude from 3.8 mV distally to 1.0 mV proximally below the elbow (74% amplitude loss), with slight increase in duration (Figure C18-1B). Also, the right ulnar CMAP amplitude dropped from 4.2 mV to 1.0 mV (76% amplitude loss). The CMAP amplitude decay of these nerves was also confirmed by greater than 50% concomitant drop in CMAP areas. The amplitude change of the right median nerve (from 3.3 mV distally to 2.7 mV proximally) was borderline (18%) and probably not significant.









The clinical and EDX findings are consistent with chronic, progressive, acquired, demyelinating sensorimotor polyneuropathy because of the following:







This EDX study is not compatible with multifocal motor neuropathy with conduction block because of abnormal (unevokable) SNAPs. The polyneuropathy is obviously not acute (such as with Guillain-Barré syndrome) based on the history of slow progression (longer than 3 months) and the MUAP changes which are consistent with chronic reinnervation. The conduction slowing in the inherited demyelinating polyneuropathy, such as in Charcot-Marie-Tooth disease (CMT) type I (HMSN I), is uniform and there are no conduction blocks. Finally, the nerve conduction studies are not consistent with Charcot-Marie-Tooth disease type 2 (also called HMSN type II), because this latter disorder is a manifestation of a primary axonal polyneuropathy.



DISCUSSION



Clinical Features



Peripheral Polyneuropathies


Peripheral polyneuropathy is a common presenting illness in neurologic practice with multiple, sometimes overwhelming, list of potential etiologies. Pattern recognition is a useful diagnostic approach but applies to a minority of patients who usually have advanced disease and often requires vast clinical experience such as by a seasoned neurologist. For an example, an asymmetrical polyneuropathy with predilection to cool skin areas (nipples, buttocks, and fingers) and skin ulcerations is highly suggestive of leprous neuropathy. Also, a distal sensory polyneuropathy with brisk reflexes, mild cognitive impairment, and a red tongue suggests combined system degeneration due to vitamin B12 deficiency. Another approach to the etiologic diagnosis of peripheral polyneuropathy is to order all available tests, including costly serology evaluations, on every patient with a polyneuropathy. Unfortunately, this irrational “shotgun” approach is quite common and often utilized by internists and some neurologists. It sometimes results in an incorrect diagnosis secondary to incidental abnormalities such as an elevated glucose on glucose tolerance test or antineuronal antiboby on serological testing.


A recommended and more rational approach may be initiated on every patient presenting with a peripheral polyneuropathy. This could be achieved by performing a thorough history and physical examination followed by EDX studies (see Figure C26–1, Case 26), and often results in limited and cost effective investigations (Table C18-1). Despite extensive investigations in specialized centers that includes EDX testing, antibody panels and genetic testing, up to 20% of patients with peripheral polyneuropathies will not have their exact causation identified. Of those with idiopathic etiology, it is estimated that a familial neuropathy accounts for about 40% if a meticulous family history is taken and relatives are carefully examined.


Table C18-1 Essential Facts Important in the Classification and Etiologic Diagnosis of Peripheral Polyneuropathy





































CIDP = chronic inflammatory demyelinating polyradiculoneuropathy, HNPP = hereditary neuropathy with liability to pressure palsy, CMT = Chercot-Marie-Tooth disease, HIV = human immunodeficiency virus.


* Include diabetes mellitus, uremia, thyroid disorders.



Chronic Demyelinating Polyneuropathies


In most peripheral polyneuropathies, it is often possible to define the predominant pathophysiologic mechanism, based on electrophysiologic and pathologic features, as being either primarily axonal or demyelinating. In demyelinating polyneuropathy, it is also useful to distinguish between neuropathies with segmental (multifocal) versus uniform slowing, based on electrophysiologic studies (see electrodiagnosis). Multifocal or segmental demyelinating polyneuropathies are almost always acquired, while uniform demyelinating polyneuropathies are typically hereditary.


The causes of chronic axonal neuropathies are abundant, while chronic demyelinating polyneuropathies have a fairly restrictive differential diagnosis (Table C18-2). Many acquired demyelinating polyneuropathies are immune in nature and respond to immunosupression or immunomodulation, while most axonal polyneuropathies are metabolic or toxic in nature. Since the differential diagnosis of chronic acquired demyelinating polyneuropathies is quite limited, the diagnostic work-up for patients with such entities is much less laborious and is quite different from that of patients with axonal neuropathies (Table C18-3).


Table C18-2 Common Causes of Chronic Demyelinating Peripheral Polyneuropathy







Acquired (nonuniform multifocal slowing)





Hereditary (uniform slowing)







CIDP = chronic inflammatory demyelinating polyradiculoneuropathy; HIV = human immunodeficiency virus; GM1 = ganglioside M1; MAG = myelin-associated glycoprotein; MGUS = monoclonal gammopathy of unknown significance; Ig = immunoglobulin; POEMS syndrome = polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes; HMSN = hereditary motor and sensory neuropathy; CMT = Charcot-Marie-Tooth disease; HNPP = hereditary neuropathy with liability to pressure palsy.


* May have multifocal slowing also, usually across common entrapment sites.


Table C18-3 Recommended Work-Up of Chronic Acquired Demyelinating Peripheral Polyneuropathy






Stay updated, free articles. Join our Telegram channel

Aug 12, 2016 | Posted by in CARDIOLOGY | Comments Off on Case 18

Full access? Get Clinical Tree

Get Clinical Tree app for offline access