HISTORY AND PHYSICAL EXAMINATION

Fever, malaise, and sore throat developed in a 55-year-old woman who was otherwise in excellent health. She was treated with antibiotics and analgesics. Six days later, she first noticed that her legs had “buckled” underneath her. That afternoon, she had difficulty climbing steps and became aware of tingling in both hands. She awoke the next morning and could not stand. She was brought to the hospital and was admitted. Apart from a diuretic for mild hypertension, she was taking no other medications.

On physical examination, the patient was afebrile and in no apparent distress. She had normal vital signs, including blood pressure, pulse, and respiration. Neurologic examination revealed normal mental status and cranial nerves. Motor examination was relevant for weakness of the neck flexors (Medical Research Council [MRC] 4+/5), the proximal pelvic muscles (MRC 3/5), and the shoulder muscles (MRC 4-/5). Distally, she performed much better (5-/5). Deep tendon reflexes were absent throughout. Sensory examination was normal, except for mild impairment of touch and pin sensation in both hands. She was unable to sit or stand independently.

An electrodiagnostic (EDX) examination was performed 3 days after admission and 6 days after the onset of neurologic symptoms. This was repeated later, on the 12th day after admission, which corresponded to day 15 from the onset of neurologic symptoms. Needle electromyography was not performed due to the acute nature of the symptoms.

Please now review the Nerve Conduction Studies tables.

QUESTIONS

EDX FINDINGS AND INTERPRETATION OF DATA

The first set of nerve conduction studies (NCS), performed on day 6 from the onset of neurologic symptoms, revealed the following:

The above findings point to pathology at the spinal roots and the peripheral sensory and motor nerves, manifesting as either axonal loss or distal conduction block (as a cause of low distal CMAPs). Only one criterion of demyelination (absent F waves) is fulfilled. The absent F waves and the sural sparing pattern (i.e., abnormal upper extremity SNAPs with normal sural SNAP) are findings that are highly suggestive of GBS (see discussion).

The second study, done 9 days later (15 days from the onset of neurologic symptoms), revealed that now all hand SNAPs (median, ulnar, and radial) are abnormally low in amplitude or absent. In contrast, the sural SNAP continues to be normal. The slowing of distal latencies now is more pronounced, which fulfills one of the criteria for acquired demyelination. The F waves are still absent, fulfilling a second criterion. However, the velocities are still moderately slowed and there is no confirmed conduction block. Thus, in the second study, two criteria of acquired demyelination are fulfilled (three are required; see discussion), and the sural sparing pattern (i.e., abnormal upper extremity SNAPs with normal sural SNAP) is confirmed. These findings are strong evidence for the diagnosis of GBS.

The prognosis here is fair because of low distal CMAPs, although at no time did the mean CMAP amplitude decrease below 20% of the lower limit of normal. The first study is less helpful because the patient had not reached plateau yet and because time for the completion of wallerian degeneration has not been allowed. The second study, done a week after the patient reached plateau, reveals a mean CMAP of 39% of the lower limit of normal.

In summary, the profile of these NCSs is consistent with an acquired demyelinating polyneuropathy as seen with acute inflammatory demyelinating polyneuropathy (AIDP), the most common type of GBS. The prognosis for recovery is fair due to modest decrease in mean CMAP amplitude. A repeat EMG 3 to 5 weeks after the onset of symptoms was recommended to confirm this prognostic prediction.

DISCUSSION

Adapted from Katirji B, Kaminski HJ, Preston DC et al., eds. Neuromuscular disorders in clinical practice. Boston, MA: Butterworth-Heinemann, 2002.

Certain clinical features and diagnostic studies are useful in establishing the correct diagnosis:

Clinical Features

Guillain-Barré syndrome (GBS), also known as Landry-Guillain-Barré-Strohl syndrome, is the most common cause of subacute flaccid paralysis in the world. It is a generalized disorder of the peripheral nervous system that is characterized by multiple limb and cranial muscle weakness with areflexia. It has an incidence of slightly less than 2 per 100 000 population. Guillain-Barré syndrome is frequently preceded by a viral or bacterial illness, usually an upper respiratory infection or gastroenteritis.

Typically, GBS develops over the course of a few days. Limb weakness appears simultaneously with a slight tingling and impairment of sensation in the hands and feet. The sensory symptoms are rarely painful while myalgia and back pain are common. Weakness usually ascends from the lower limbs to the upper limbs and, sometimes, to the cranial nerves. Less commonly, the weakness in GBS is descending. Facial weakness occurs in approximately one half of patients, and respiratory failure requiring mechanical ventilation occurs in one-third. Typically, progression lasts up to 4 weeks, while progression exceeding 4 weeks suggests an alternative diagnosis, such as chronic inflammatory demyelinating polyneuropathy (CIDP). Cerebrospinal fluid protein usually rises during the second week of illness, without pleocytosis (albuminocytologic dissociation). The presence of CSF pleocytosis is not incompatible with GBS, but if it is significant (>50 cells), other diagnoses, particularly infection with the human immunodeficiency virus (HIV), should be suspected. The frequency of various GBS manifestations is shown in Table C23-2.

Table C23-2 Frequency of Features and Clinical Variants of Acute Guillain-Barré Syndrome

* Variants are associated with diminished reflexes, demyelinating features as detected on electrophysiologic studies, and elevated cerebrospinal concentrations of fluid protein. Frequencies shown are those found in fully developed illness.

From Ropper AH. The Guillain-Barré syndrome. N Engl J Med 1992;326:1130–1136, with permission.

Because of its similarity to its animal analogue, experimental allergic neuritis, GBS was considered to be a single disorder characterized by an acute immune attack on myelin, hence the term acute inflammatory demyelinating polyneuropathy (AIDP). As the name implies, AIDP is characterized by prominent demyelination and inflammatory infiltrates in the spinal roots and nerves. Criteria for the diagnosis of GBS are based on the AIDP prototype and include both clinical and laboratory findings (Table C23-3). Until recently, AIDP had been used interchangeably with GBS. However, it is now well recognized that axonal forms of GBS exist. Several studies during the last two decades have documented that, although most cases of GBS are characterized by segmental demyelination, many patients with typical GBS have evidence of primary axonal degeneration (“axonal” GBS). GBS may be due to a pure motor axonopathy, named acute motor axonal neuropathy (AMAN), or a mixed sensorimotor axonopathies, named acute motor sensory axonal neuropathy (AMSAN) (Table C23-4). In addition to their electrophysiologic characteristics, the subtypes of GBS have characteristic pathological findings, with evidence of vesicular demyelination in AIDP and axonal phagocytosis in AMAN and AMSAN. Also, there is a strong association between GBS, particularly the AMAN form, with a preceding Campylobacter jejuni infection and the presence of serum antibodies directed toward ganglioside M1 (anti-GM1).

Table C23-3 Diagnostic Criteria for Guillain-Barré Syndrome (Mainly Acute Inflammatory Demyelinating Polyradiculoneuropathy)

CSF = cerebrospinal fluid; CSN = central nervous system; NCV = nerve conduction velocity; NCS = nerve conduction studies.

Modified from Asbury AK, Cornblath DR. Assessment of current diagnostic criteria for Guillain-Barré syndrome. Ann Neurol 1990;27(Suppl): S21–S24.

Table C23-4 Classification of Guillain-Barré Syndrome

In addition to the three major subtypes of GBS, many variants of the typical GBS presentation exist. Among them, Miller-Fisher syndrome is the most widely known. It consists of ophthalmoplegia, ataxia, and areflexia. Others include a pure sensory form, an ataxic form, a pharyngeal–cervical–brachial regional form, and a pure autonomic form. Thus, GBS is a syndrome that encompasses many disorders with similar clinical presentations but likely with different etiologies and pathophysiologies (Tables C23-2 and C23-4).

Plasma exchange (PE) is the first and only treatment that has been proven to be superior to supportive treatment alone in GBS. This is based on six randomized trials, all comparing PE versus supportive treatment alone. The number of effective PEs was compared in two randomized trials. In mild GBS, two PEs are significantly superior to none, and in moderate or severe GBS, four sessions are significantly superior to two, while additional PEs (such as six) do not provide any additional benefit. Plasma exchange is more beneficial when started within seven days after disease onset rather than later, but is still beneficial in patients treated up to 30 days after disease onset. Intravenous immunoglobulin (IVIG) also hastens recovery from GBS and is equivalent to plasma exchange, based on three randomized trials that compared IVIG to plasma exchange. Administering IVIG after plasma exchange is not significantly better than plasma exchange alone. Also, corticosteroids are ineffective and adding methylprednisolone to IVIG treatment provides no additional benefit.

Most patients with GBS ultimately recover, but the prognosis is extremely variable. The plateau phase usually lasts several days or weeks but may persist for months in severe cases with quadriplegia and respiratory failure. The mortality rate has declined with the advent of critical care units and has ranged from 2 to 10%, mostly due to pulmonary embolism and cardiac arrhythmia (Figure C23-1). Approximately 20% of patients have permanent disability, and 10% of these are severely disabled. Advanced age, history of preceding diarrheal illness, recent CMV infection, rapid evolution of weakness, prolonged plateau before recovery, and ventilator dependency predicts a poor prognosis. Patients with AMSAN have the worst prognosis, while patients with AMAN surprisingly have a prognosis and recovery rate similar to patients with AIDP, despite electrophysiologic and pathologic evidence of axonal degeneration. This is best explained by a distal motor axonal loss (intramuscular motor nerve terminals) and rapid reinnervation. The best prognostic indicator of poor outcome is an average CMAP amplitude at plateau of less than 20% of the lower limit of normal. To rule out distal demyelination (i.e., distal conduction block) as a cause of low CMAP amplitudes, sequential EDX studies are often required.

Figure C23-1 Bardycardia alternating with tachycardia in 35-year-old man with severe quadriplegia and bifacial weakness due to GBS.

Electrodiagnostic Features

Diagnostic Role of Electrodiagnostic Evaluation

The EDX study, and in particular its nerve conduction studies (NCS) component, is the most important ancillary method available to confirm the diagnosis of GBS. Yet, the electrodiagnosis of GBS continues to be a challenging task and is subject to errors that depend on the number of nerves studied and the experience of the electromyographer. The electrophysiologic evaluation of patients with GBS reveals a wide range of abnormalities caused by multifocal demyelination, axonal degeneration, or both. However, because of the patchy nature of demyelination in AIDP and its predilection to very proximal and very distal nerve segments (spinal roots and intramuscular branches, retrospectively), the EDX studies are not infrequently normal or reveal nonspecific neuropathic findings that are insufficient for a definite diagnosis, particularly when done during the first few days or weeks of disease onset. Also, the diagnosis of the axonal forms of GBS, AMAN and AMSAN, depends mostly on findings evidence of axonal loss without significant demyelination. In AMAN, which is associated with normal SNAPs, it is difficult to distinguish the disorder from a subacute axonal polyradiculopathies that also spare the SNAPs such as carcinomatous meningitis. In AMSAN, the presence of a mixed sensorimotor axonal polyneuropathy may be impossible to distinguish, based on EDX studies only, from other causes of subacute axonal polyneuropathies such as critical illness polyneuropathy or polyneuropathies associated with porphyria, or drug or environmental toxins.

The prompt and early diagnosis of GBS is warranted by the need to initiate early treatment. Hence, the EDX studies are most useful and often requested during the first 1–2 weeks of illness, soon after presentation or admission to the hospital. During this critical period, 5–10% of patients unfortunately have normal studies (despite severe weakness). Another 5–10% have only nonspecific nerve conduction abnormalities, such as mild slowing, absent and/or prolonged H reflexes or F waves (due to spinal root demyelination), or low-amplitude CMAPs (due to intramuscular motor nerve terminals involvement).

AIDP, the most common form of GBS, is characterized by multifocal demyelination, a required finding for definite diagnosis. Electrodiagnosis of AIDP has traditionally relied on abnormal motor NCS, such as conduction block, CMAP dispersion, delayed or absent F waves, and slowing of latencies and velocities. It is now clear that sensory NCSs are also important in providing electrodiagnostic evidence that might distinguish primary demyelinating from primary axonal polyneuropathy.

Motor Nerve Conduction Studies

Electrophysiologic evidence of definite demyelination requires the presence of demyelination in at least two motor nerves with no evidence of coexisting entrapment syndromes. During the first two weeks of illness, slowing of conduction velocity in the demyelinating range (e.g., less than 70–80% of the lower limits of normal) is present in less than 25% of patients. Conduction block in one or more motor nerves, a strong evidence for acquired demyelination, is present in less than 30% of patients (Figure C23-2).

Figure C23-2 Median motor conduction block and slowing on day 4 in a 25-year-old patient with GBS. Note the significant drop of CMAP amplitude (80%) and area (74%) between distal stimulation (upper tracing) and proximal stimulation (lower tracing) with marked slowing of proximal conduction velocity (19 m/s).

Sensory Nerve Conduction Studies

There is relative preservation of the SNAPs compared to the CMAPs, especially in the first 2–3 weeks of illness. The most common abnormalities seen in GBS are reduced SNAP amplitudes associated with variable slowing of the sensory distal latencies. The combination of normal sural SNAPs and low-amplitude or absent upper-extremity SNAPs (“sural-sparing pattern”) is common and distinctive of acquired demyelinating polyneuropathy, including AIDP. This finding, which is highly specific (96% specific) for the diagnosis of AIDP, is present in about half of the patients with AIDP and in about two-thirds of patients younger than 60 years. The exact cause of relative preservation of sural SNAP compared to the median and ulnar SNAPs may be due to relative resistance of the larger-diameter myelinated fibers in the sural trunk compared to the smaller tapering nerve fibers in the digital nerves of the hands. Also, this finding may reflect the lack of length-dependent axonal degeneration as seen with axonal polyneuropathy.

Limitations of the sural sparing pattern include that a pre-existing carpal tunnel syndrome may result in abnormally low amplitude or absent median and normal sural SNAPs. Hence, the sural sparing pattern should depend on at least two abnormally low-amplitude or absent hand SNAPs and normal sural SNAPs. Another limitation is that the sural SNAP is either low in amplitude or absent in elderly or obese patients, and in those with polyneuropathy. Technical considerations in hospitalized patients, especially those with quadriparesis or on mechanical ventilation in the intensive care units, also render studying sural SNAP difficult. In these cases, it is useful to assess the radial SNAP, since the median and ulnar SNAPs are more preferentially affected that the radial and sural SNAP. We found that a high sensory ratio (sural + radial SNAPs/median + ulnar SNAPs >1) is also strong evidence that support the diagnosis of AIDP. For example, we found that AIDP is 12 times more likely to have a sensory ratio of greater than 1 compared to diabetic neuropathy.

Late Responses

An absent tibial H reflex is the most common finding in patients with AIDP, being detected in about 95–100%. However, an absent H reflex is equivalent to an absent ankle jerk and is not specific (35% specificity) for AIDP as it is absent in most polyneuropathies as well as S1 radiculopathies and elderly subjects. Absent or impersistent F waves or delayed minimal F wave latencies are present in 40–80% of patients with AIDP but are, similar to the H reflex, nonspecific (33% specificity), since they accompany most peripheral polyneuropathies as well as radiculopathies and mononeuropathies. Absent or delayed minimal F wave latencies are most valuable when accompanied by normal or relatively preserved motor nerve conduction studies, a finding that is considered evidence of proximal demyelination (Figure C23-3). Another useful abnormality is the identification of A (axon) waves. Though A waves may be seen in up to 5% of asymptomatic individuals, particularly while studying the tibial nerve, recording multiple or complex A waves from several nerves is commonly associated with demyelinating polyneuropathies such as AIDP (Figures C23-4 and C23-5). The exact pathway of the A wave is unknown but it may be generated as a result of ephaptic transmission between two axons with the action potential conducting back down the nerve fiber to the muscle.

Figure C23-3 Median minimal F wave latencies in a 30-year-old healthy subject (A) and a 35-year-old patient with GBS (B). Note the marked slowing of minimal F wave latencies (arrows) in the patient compared to control.

Figure C23-4 A wave recorded from the abductor pollicis brevis (arrows) stimulating the median nerve at the wrist in a 65-year-old man with GBS. The A waves shown in a raster mode (A) and superimposed mode (B) have a constant morphology and latency, best explained by the fixed point of ephapse. Note the absence of median F waves.

Figure C23-5 Complex A wave recorded from the abductor hallucis (arrows), stimulating the tibial nerve at the ankle in a 65-year-old man with GBS. The A waves are shown in a raster mode (A) and superimposed mode (B).

Diagnostic Criteria

Since AIDP is the most common type of GBS, the EDX criteria of GBS depend mostly on identifying segmental demyelination of peripheral nerves. The presence of conduction block, significant temporal dispersion, marked slowing of motor distal latencies, conduction velocities or F wave latencies are necessary findings for definite segmental demyelination. When the findings are multifocal or associated with conduction blocks or both, they are strong evidence for an acquired demyelinating neuropathy such as AIDP. Several NCS patterns emerge in patients with GBS ranging from normal studies to studies that are diagnostic of AIDP (Table C23-5).

Table C23-5 Common Nerve Conduction Patterns in Guillain-Barré Syndrome

Normal nerve conduction studies Absent H reflexes Prolongation or absent F waves Patchy, mild slowing of distal latencies and conduction velocities Low-amplitude CMAPs and SNAPs Distal CMAPs dispersion Absent/low-amplitude upper extremity SNAPs, with normal sural SNAP Sensory ratio (sural + radial SNAPs/median + ulnar SNAPs) more than 1 Single conduction block/temporal dispersion Prominent multifocal motor and sensory slowing, with multifocal conduction blocks

CMAP = compound muscle action potential; SNAP = sensory nerve action potential.

Several criteria have been proposed and none are universally accepted, some with strict definitions for demyelination and others with less rigid demands (Table C23-6). There are several limitations to the various EDX criteria for GBS. First, the exact cutoff of conduction velocities and distal latencies for establishing the diagnosis of primary demyelination and excluding axon loss disorders continues to be controversial. This is particularly true when the distal CMAPs are diminished below the lower limit of normal (LLN). It is clear that using the LLN for velocities or upper limit of normal for distal latencies as cutoffs is incorrect since many axonal neuropathies result in some degree of slowing. The available criteria were mostly based on consensus among groups of physicians. Earlier criteria assessed only velocities with no regards to CMAP amplitudes. More recently, Alberts and Kelly have used conduction velocity slowing of less than 90% of the LLN when CMAP amplitude is above 50% of LLN and less than 80% of the LLN when CMAP amplitude is below 50% of LLN. Asbury and Cornblath suggested conduction velocity slowing of less than 80% of LLN if the CMAP amplitude is greater than 80% of LLN and less than 70% of LLN if CMAP amplitude is greater than 80% LLN. There are no available criteria for the cutoff slowing when CMAP amplitude is very low, such as less than 20% of LLN, in order to distinguish severe axonal loss from segmental demyelination. Because of the differences of these EDX criteria, there is a considerable varaiation in the number of patients who would fulfill the criteria for AIDP (Figure C23-6). This has also resulted in disagreements between physicians and, sometimes, unfortunate misdiagnoses. The second limitation to these criteria is that the available criteria considers only the motor nerve conduction studies despite good evidence that sensory studies are important in the diagnosis of GBS and their use should be emphasized. These include the sural sparing pattern and an increased sensory ratio (sural + radial SNAPs/median + ulnar SNAPs) of more than 1.

Table C23-6 Two Commonly Used Electrodiagnostic Criteria for Definite Acquired Demyelinating Polyneuropathy Including AIDP

Criteria	Albers and Kelly	Asbury and Cornblath
Required	≥3 criteria	≥3 criteria
Conduction block and/or temporal dispersion	? Number of nerve*	in ≥1 nerve*
Slowing of MCV	in ≥2 nerves	in ≥2 nerves
	<90% LLN if CMAP amplitude >50% LLN	<80% LLN if CMAP amplitude >80% LLN
	<80% LLN if CMAP amplitude <50% LLN	<70% LLN if CMAP amplitude <80% LLN
Slowing of MDL	in ≥2 nerves	in ≥2 nerves
	>115% ULN if CMAP amplitude is normal	>125% ULN if CMAP amplitude >80% LLN
	>125% ULN if CMAP amplitude is <LLN	>150% ULN if CMAP amplitude <80% LLN
F wave latency	in ≥1 nerve	in ≥2 nerves
	>125% ULN	Absent, or latency
		>120% ULN if CMAP >80% LLN
		>150% ULN if CMAP >80% LLN

CMAP = compound muscle action potential; LLN = lower limit of normal; MCV = motor conduction velocity; MDL = motor distal latency; ULN = upper limit of normal.

* Conduction block = >30% decrease in CMAP amplitude between distal and proximal stimulations. Conduction block = >20% decrease in CMAP area or amplitude between distal and proximal stimulations, with <15% increase in CMAP duration; temporal dispersion = >20% decrease in CMAP area or amplitude between distal and proximal stimulations, with >15% increase in CMAP duration.

Adapted from Brown WF. Acute and chronic inflammatory demyelinating neuropathies. In: Brown WF, Bolton CF, eds. Clinical electromyography. Boston, MA: Butterworth-Heinemann, 1993.

Figure C23-6 The percentage of patients with GBS fulfilling six various EDX criteria for AIDP (see Suggested Readings list) from a total of 43 patients with GBS in the first 4 weeks of illness.

(Adapted from Alam TA, Chaudhry V, Cornblath DR. Electrophysiological studies in the Guillain-Barré syndrome: distinguishing subtypes by published criteria. Muscle Nerve 1998;21:1275–1279.)

It is clear that criteria with graded probability and various level of certainty for AIDP are needed, since the disorder has a wide range of EDX manifestations that may also change with time due to ongoing disease or due to the effect of remyelination or wallerian degeneration. Our recently published graded criteria utilized, in addition to one criteria of definite demyelination by Asbury and Cornblath, other nerve conduction abnormalities including absent/slowed F waves and sural sparing pattern. These criteria confirmed the diagnosis of AIDP in the first 2 weeks of illness with high specificity and a positive predictive value of 95–100% and with moderate sensitivity in about 65% of patients (Table C23-7).

Table C23-7 Diagnostic Power of Findings on Nerve Conduction Studies in Guillain-Barré Syndrome

Sequential studies, particularly in the first several weeks of illness, are valuable tools in GBS. The pathological process in GBS is dynamic during the early few weeks that a single EDX sampling may not be sufficient to establish the diagnosis. Unfortunately, many patients are now discharged to rehabilitative facilities before the third week of illness, and sequential studies are often not requested because clinical decisions have already been made and treatment has begun. However, there are several advantages of sequential studies:

1. During the first 2 weeks of illness, only 30 to 50% of patients with AIDP fulfill the criteria for demyelination, compared with 85% by t he third week (Figure C23-7). About 10% of patients with AIDP never fulfill the criteria for demyelination.

2. Low or absent CMAPs and/or SNAPs are considered signs of axonal loss as seen with AMAN and AMSAN. However, a rapid improvement of CMAP or SNAPs amplitudes over a few weeks is occasionally observed on sequential studies. This finding is consistent with distal motor or sensory nerve demyelination and subsequent remyelination. These AIDP patients, who have good prognosis, will have early EDX studies that are misdiagnosed as axonal GBS unless sequential studies are performed.

3. In AMAN and AMSAN, the motor CMAPs are low in amplitudes with no or minimal slowing of distal latencies and conduction velocities. Occasionally, conduction block may be detected early on which suggest demyelination and a diagnosis AIDP. However, sequential studies prove in these patients that the conduction block was due to axonal loss (axonal noncontinuity, early axon loss, or axon-discontinuity conduction block) and the disorder is in fact an axonal GBS (Figure C23-8).

Figure C23-7 Electrodiagnostic power of sequential nerve conduction studies in the diagnosis of AIDP during 50 weeks of illness. Note that the study is often diagnostic in the third and fourth weeks of illness and is least diagnostic after 25 weeks.

(Adapted from Albers JW, Donofrio PD, McGonagle TK. Sequential diagnostic abnormalities in acute inflammatory demyelinating polyradiculopathy. Muscle Nerve 1985;8:528–539.)

Figure C23-8 Median motor conduction study in a 75-year-old patient with axonal GBS, compatible with AMAN, done 5 days (A) and 30 days (B) after the onset of ascending quadriparesis that reached its nadir on day 7. Note the median conduction block in the forearm on day 5 (A) with significant (>50%) drop in CMAP amplitude and area between distal stimulation (upper tracing) and proximal stimulation (lower tracing). Subsequent study on day 30 (B) showed a significant decline of the distal motor CMAP which now almost equals the proximal CMAP. The initial block is consistent with the so-called axonal noncontinuity, early axon loss, or axon-discontinuity conduction block. This type of conduction block is only confirmed after a repeat study following the completion of wallerian degeneration. Recall that in wallerian degeneration, the distal CMAP decreases in amplitude starting 1–2 days after acute nerve insult and reaches its nadir in 5–6 days.

A small percentage of patients have axonal GBS, namely AMAN and AMSAN. These axonal subtypes of GBS are typified by the loss of CMAP (and SNAP in cases of AMSAN) amplitudes without significant slowing of distal latencies, F wave latencies, or conduction velocities, and by the absence of conduction blocks or temporal dispersion. This contrasts with AIDP which is characterized by slowing of both distal latencies and conduction velocities, with conduction blocks and temporal dispersion and relative preservation of CMAP and SNAP amplitudes.

FOLLOW-UP

Vital capacity on presentation was borderline at 2.6 L. Lumbar puncture was performed on the admission date, 2 days after the onset of neurologic symptoms. Cerebrospinal fluid protein was 57 mg/dL without pleocytosis. The patient was treated with a plasma exchange the next morning, 3 days after the onset of symptoms. A total of four plasma exchanges were administered over one week. Despite this, the patient’s neurologic condition deteriorated to complete quadriplegia and mild bilateral facial weakness. However, respiration was maintained without the need for mechanical ventilation. Vital capacity reached a nadir of 1.8 L. Repeat CSF examination 2 weeks after the onset of neurologic symptoms revealed markedly elevated CSF protein at 753 mg/dL without pleocytosis.

The patient lingered at a plateau for approximately 1 week before showing early signs of recovery. With rehabilitation, she improved gradually, first in the distal hand and foot muscles, then in the upper limbs, and finally in the lower limbs. She was able to feed herself 6 weeks after the onset of illness, sat independently at 2 months, and ambulated with a walker at 3 months. Four months after onset, the patient was ambulating independently but demonstrated mild residual hip flexor weakness (MRC 4+/5). She still was diffusely areflexic.

ANSWERS

1. D; 2. D; 3. B.