# Serum False-Positive Botulism in Guillain-Barré Syndrome

Authors: Yen-Chi Yeh; Kon-Ping Lin; Kuan-Lin Lai; Jen-Feng Liang; Kwong-Kum Liao
Journal: Scholarly Research Exchange
 (2008)

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## Abstract

A 30-year-old man of Guillain-Barré syndrome (GBS) had atypical descending weakness and history of exposure to expired canned meat, which caused confusion with botulism. His serum showed false-positive botulism type B by the standard mouse bioassay. The diagnosis of axonal GBS was based on clinical and electrophysiological evidence. This report highlights the fact that GBS can present descending weakness and serum false-positive botulism.


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## Body

## 1. Introduction

Botulism is a potential  lethal
neuromuscular junction disease caused by botulinum neurotoxin. It is
characterized by the acute onset of symmetric, descending paralysis with prominent
bulbar palsies, which usually starts from ocular musculature. The autonomic dysfunctions are prominent. Guillain-Barré syndrome (GBS), an immune-mediated neuropathy, exhibits a similar clinical picture as
botulism. Rapidly progressive weakness and areflexia often lead to bulbar and
respiratory compromise. GBS usually presents ascending weakness, but atypical
distribution of weakness can be observed
occasionally. Herein, we report
a case of axonal GBS with atypical descending pattern of weakness and serum false-positive botulism type B,
which makes a diagnostic challenge.
We discuss the differential diagnosis for these two potential lethal diseases
based on the clinical, electrophysiological, laboratory evidences.


## 2. Case Report

A 30-year-old man ate expired
canned meat on 23 December 2007 (day 1), and then he had dizziness and
constipation on the next day.
Sore throat and mild dyspnea developed on day 3. Bulbar weakness occurred on
day 4. Descending weakness progressed in the following days from his upper
limbs to lower limbs, and he was unable to walk on day 7.He came to our hospital on day 14 because of the progressive
weakness. Upon arrival, physical examination showed dyspnea and abdominal
distension. Neurological examination revealed clear consciousness with
prominent bulbar palsies, including facial diplegia, dysarthria, dysphagia, and
dysphonia. Pupil reflexes and extraocular movements were intact. Generalized
weakness and hyporeflexia were noted. Complete blood count, serum chemistry,
urinalysis, and brain CT showed normal results. Serum, vomit, and stool samples
were sent for botulism exam. Both slow (3 Hz) and rapid (30 Hz) repetitive
nerve stimulation tests (RSTs) did not show significant abnormal results. Nerve
conduction study (NCS) showed reduction of overall compound motor action
potentials (CMAP) but relatively preserved sensory nerve
action potentials (SNAP) (Table1). Autonomic dysfunction was
indicated by decreased heart rate variation and absent sympathetic skin
response at soles bilaterally. The cerebrospinal fluid (CSF) studies
showed no significant abnormality.Table 1
The electrophysiological study results on day 14 and day 25
after onset.
(a)
Day 14
Motor
NCSDL (ms)CV (ms)Amp (mV)F (ms)Median n3.9 (3.6±0.4)162.5 (57.8±4.2)1.8 (11.9±3.7)31.6 (25.4±2.2)Ulnar n3.3 (2.8±0.4)58.3 (61.4±3.7)6.6 (11.7±3.1)28.3 (25.0±2.1)Peroneal
nNR (4.2±0.5)NR (48.6±4.4)NR (6.0±2.5)NR (44.7±3.7)Tibial n4.3 (2.9±1.0)46.9 (50.5±5.3)2.6 (13.1±5.0)50.6 (45.0±4.8)Sensory
NCSDL (ms)Amp (μV)Median n2.4 (2.5±0.2)59.8 (33.0±13.4)Ulnar n2.5 (2.5±0.2)31.2 (26.1±12.0)Sural n3.2 (3.0±0.3)6.1 (12.5±5.2)(b)
Day 25
Motor
NCSDL (ms)CV (ms)Amp (mV)F (ms)Median n5.253.41.230.3Ulnar n4.152.95.727.6Peroneal
nNRNRNRNRTibial n5.845.81.052.1Sensory
NCSDL (ms)Amp (μV)Median n2.751.4Ulnar n3.030.4Sural nNRNRNeedle
EMGRestRecruitmentPolyphasicIns ActPSWFibMUAPBrachioradialisIncreased2+2+ReducedIncreasedVastus
medialisIncreased2+2+ReducedIncreasedGastrocnemiusIncreased3+3+ReducedIncreasedT
paraspinal muscleIncreased2+2+ReducedIncreasedAmp =
amplitude, CV = conduction velocity, DL = distal latency, EMG  =
electromyography, Fib = fibrillation,F = F latency, Ins Act = insertion activity, MUAP = motor unit action
potential, n  = nerve, NCS = nerve conduction study, NR = no response, PSW =
positive sharp wave, T = thoracic.
1Normal value
(mean ± standard deviation) [2].The symptoms worsened gradually. The
patient complained of distal paresthesia with sensory disturbances in position
and light touch modalities over his toes. All limbs failed to achieve antigravity strength on day 16. Because respiratory distress
ensued, endotracheal intubation with mechanical ventilation was applied. Serum
positive botulism was reported but with undetermined subtype on day 20. The
subacute disease course, sensory dysfunction, and normal RST favored GBS over botulism. The patient underwent 6 sessions of
plasmapheresis and recovered gradually.Botulism
type B was detected in serum by standard mouse bioassay, but the cultures of
both vomit and stool were negative forClostridium
botulinum [1]. The
follow up of NCS on day 25 showed
profound reduction of CMAP and SNAP. EMG revealed spontaneous denervation
activities in all the muscles sampled at limbs and trunk, compatible with
polyradiculoneuropathy with axonal degeneration (Table 1).


## 3. Discussion

It seems that our patient had
axonal GBS with serum false-positive botulism. History of exposure to high-risk
food, the clinical course of descending weakness, and presentation of autonomic
dysfunction led to the possibility of botulism.
However, the follow up of
electrophysiological studies confirmed its diagnosis as GBS.Both GBS and botulism are critical
issues for patients with rapid onset of flaccid paralysis, which can result in
respiratory failure. Early diagnosis of botulism is very important, because
adequate treatment decreases morbidity and mortality. The diagnosis is based on
positive laboratory studies ofClostridium
botulinum and its exotoxin [1].
The mouse bioassay remains the gold standard test for biologically active
neurotoxins. However, this method has some disadvantages and may result in
errors in clinical practices. First, mice can die nonspecifically during the
procedure.Serum false-positive botulism via mouse bioassay has been reported
in GBS and Miller-Fisher syndrome (MFS)
[3, 4]. Second, the standard mouse bioassay requires 4 days, but
antitoxin should be given as soon as possible. Several rapid in vitro assays,
such as immunological methods, molecular detection, and genetic
characterization, have been developed to confirm the
mouse bioassay but are not widely available [1].Clinical symptoms and signs cannot
offer enough information for distinguishing botulism from GBS, especially the
motor-predominant variants. Autonomic dysfunctions develop in both diseases,
which confuse clinical physicians further. Some GBS have descending weakness
instead of the typical ascending pattern
[5]. In this situation, ocular manifestations play a key role at initial stage. The acute
descending paralysis of botulism usually begins in ocular musculature with
presentation of impaired accommodation (100%), reduced pupil light reflex
(83%), and diplopia (44%) [6].
In contrast, GBS relatively spares the eyes, except variants with prominent
ophthalmoplegia such as MFS. However, one case who had GBS mimicking botulism with ophthalmoplegia as the initial symptom of the descending
paralysis has been reported [7]. Patients of MFS combined with autonomic dysfunctions are
indistinguishable from botulism clinically, especially those with rare pupil
involvement [8].Electrophysiological, CSF, and
immunological studies are also necessary for differential diagnosis.
Electrophysiological studies give early clues for botulism. Rapid (20 to 50 Hz)
RST shows incremental responses
in more than 60% of patients [9].
Instead, classic electrophysiological findings of GBS may not be evident within
2 to 4 weeks. CSF studies may not be diagnostic within 2 weeks. Positive
anti-ganglioside antibodies favor GBS, and anti-GQ1b presents in more than 85%
of patients with MFS, but these two methods are not popular in all hospitals [5].We believe this
case is the first report of
axonal GBS with history of
exposure to high-risk food, descending weakness, and serum false-positive
botulism via mouse bioassay.
Clinicians should pay attention to all the
possible potential confusion.



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*Source: 430531-2008-10-23.xml*