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The "Spray Can" Sign
Validation of a Clinical Observation in Chronic Inflammatory Demyelinating Polyneuropathy
Sean J. Pittock, MD, MRCPI;
Dara Meldrum, MSc;
Orla Hardiman, MD, FRCPI
Arch Neurol. 2002;59:1637-1640.
ABSTRACT
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Background The presentation of chronic inflammatory neuropathies is variable. The
decision regarding when to intervene with treatment is ideally determined
by identifying early markers of loss of function.
Objective To test the hypothesis that an observation of functional impairment,
defined by a patient with demyelinating neuropathy, can be used as a reproducible
and reliable measure of improvement with intravenous immune globulin.
Design A 28-year-old woman presented with a chronic inflammatory demyelinating
polyneuropathy. Her first complaint was the inability to use her deodorant
spray because of hand weakness. A calibrated pincer gauge fixed on top of
her usual spray can was used to objectively test finger flexion. Tip grip
and lateral pinch were also measured. A calibrated dynamometer was used to
measure grip strength.
Results Power and precision grip force were reproducible in normal control subjects
by means of the spray can test. This test proved to be a reliable indicator
of reduced muscle strength in the patient and improved after treatment with
intravenous immune globulin.
Conclusions The spray can test objectively quantified the daily function, nominated
by the patient, of operating an aerosol can. This measurement, drawn from
a functional loss observed by the patient, proved to be a portable and reliable
indicator of decline and recovery in chronic inflammatory demyelinating polyneuropathy.
INTRODUCTION
INTRAVENOUS (IV) immune globulin has been previously shown to be an
effective and safe treatment for selected patients with acquired demyelinating
polyneuropathy.1-2 There are few
scales specifically designed for assessment of function in patients with chronic
inflammatory demyelinating polyneuropathy (CIDP). In the setting of clinical
practice, the frequency of treatments is usually determined by the patient's
subjective analysis of decline and subsequent improvement after treatment.
This is often based on the loss of a specific function, such as walking a
certain distance, that can be quantified by means of standardized measurements.
Few clinical studies have correlated specific subjective observations of weakness,
as defined by individual patients, with an objective reproducible measurement.
Comparative studies between IV immune globulin treatment and other therapeutic
modalities are accordingly limited by the variable degree and extent of weakness
among individual patients. The challenge is therefore to maximize the sensitivity
of the test measurement, while maintaining uniformity for statistical purposes
within the study population and limiting the time and personnel required to
perform the measurements.
REPORT OF A CASE
A 28-year-old woman presented in May 1995 with a 4-month history of
progressive weakness of her arms and legs. Her first symptom was an inability
to hold and spray her deodorant and hairspray because of weakness of the flexor
digitorum profundus and superficialis muscles of her index finger and the
intrinsic muscles of her hand. Her medical history was otherwise unremarkable.
Neurologic examination at first presentation showed marked weakness
of upper and lower limb muscles. The weakness was most marked in the distal
musculature. Manual muscle testing showed grade 4/5 weakness in infraspinatus
and biceps and 3/5 in wrist flexors and extensors and in the small muscles
of her hands. Hip flexors were grade 4/5 and ankle dorsiflexors were 4-/5
on the left and 4/5 on the right. Plantar flexors were 4/5 on the left and
5-/5 on the right. She was areflexic throughout. She had reduced sensation
to light touch and pinprick below the knees bilaterally and mild reduction
of vibration sensation to the ankles bilaterally.
The cerebrospinal fluid showed an elevated protein level (145 mg/dL)
and was otherwise normal. Electrophysiologic studies confirmed the presence
of a demyelinating sensory and motor polyneuropathy. There was abnormal temporal
dispersion in the median and ulnar nerves at the forearm bilaterally, and
in the tibial and peroneal nerves in the lower extremities. Conduction velocity
was significantly reduced throughout (eg, 25 m/s in the right median forearm,
30 m/s in the left ulnar forearm, 37 m/s in the left peroneal, and 26 m/s
in the right tibial), and distal motor latencies were markedly prolonged.
F responses were absent in the peroneal and tibial nerves bilaterally. Sensory
nerve conduction velocities were similarly slowed. Other possible causes of
neuropathy were excluded. A diagnosis of chronic inflammatory demyelinating
neuropathy was made.3
The patient began a 5-day course of IV immune globulin (0.4 g/kg per
day), and her strength gradually improved during the following 2 to 3 weeks
to a point where she could walk normally and could reengage in all activities
of daily living. She reported that the first indicator of improvement was
a return of ability to spray her deodorant can.
At most recent follow-up, 7 years after diagnosis, the patient was in
full-time employment as an accountant and was undergoing a 3-day infusion
of IV immune globulin (0.4 g/kg per day) at 6- to 8-week intervals. Each relapse
was characterized by a decline in upper and lower extremity function, with
difficulty walking and poor fine movements in the upper extremities. She used
the loss of ability to spray her deodorant as an indicator of her need for
treatment and noted that recovery on each occasion was heralded by an improvement
in her ability to perform this task.
METHODS
We tested the patient's observation that her reduced ability to operate
her aerosol can heralded a decline in her clinical function, and whether this
loss of function could be used as an indicator of IV immune globulin response.
We developed a method to measure the strength required to operate her
aerosol can and constructed a system whereby hand function and strength were
assessed before, during, and 3 weeks after IV immune globulin treatment. A
calibrated pincer gauge (B&L Engineering, Tustin, Calif)4-5
was fixed on top of the spray can and the patient was asked to simulate spraying
the can and press as hard as she could with her index finger (Figure 1). The same spray can was used throughout testing. Maximal
power of hand grip was also measured with a calibrated dynamometer,4 and tip grip and lateral pinch grip strength were
measured with the calibrated pinch gauge (Table 1).
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Figure 1. The spray can apparatus. A calibrated
pincer gauge (B&L Engineering, Tustin, Calif) was fixed on top of the
spray can.
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Maximal Hand Strength in the Patient 3 Weeks After Intravenous Immune
Globulin Treatment and in Age- and Sex-Matched Control Subjects
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The reliability of our measure was assessed by means of an age-matched
group of 9 healthy females.6-7
The mean of 3 measurements was taken on 2 occasions (with a 1-hour interval
between the occasions). All statistical analysis was performed with SPSS (SPSS
Inc, Chicago, Ill).
RESULTS
Before commencement of IV immune globulin treatment, power and precision
grip forces were reduced compared with normative data for age-matched female
controls.4-5 Improvement in hand
strength occurred after IV immune globulin therapy. Improvements in "spray
can strength" were consistently concordant with improvements in hand, tip,
and lateral pinch grip strength with successive cycles of IV immune globulin
therapy. Figure 2 depicts muscle
strength during 3 cycles of treatment. Peak recovery approximated 50% to 75%
of normal hand strength (Table 1).
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Figure 2. Muscle strength (in pounds) as
measured by the spray can apparatus, calibrated pinch gauge, and handheld
dynamometer during 3 cycles of treatment. The first point on the abscissa
reflects the time at which the patient presented with symptoms of weakness
(pretreatment). During each cycle, she was treated with 3 days of intravenous
immune globulin and examined before treatment initiation (pretreatment), after
2 to 3 days of treatment, and approximately 3 weeks later.
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The spray can test gave consistent and repeatable results when performed
on the same arm in the same healthy subject on different occasions. There
was a significant intraclass correlation coefficient for the mean of the 3
measurements on 2 occasions (P<.001; r = 0.94 for the right arm and r = 0.88 for
the left arm).7
COMMENT
Measurement scales are important tools to determine effective outcomes
after treatment. Although rating scales are used most extensively in clinical
trials, validated objective measurements are also valuable in a clinical setting
where the efficacy of a therapeutic intervention may differ between patients,
or where the efficacy of the treatment in individual patients is doubtful.
Not all patients with CIDP respond to IV immune globulin, and in some cases,
the treatment becomes less effective over time. Furthermore, the required
frequency of treatments varies from patient to patient. In the absence of
a specific scale that accounts for these variables, the determination of the
frequency of treatments and/or the decision to seek alternate treatments can
be difficult.
An ideal scale should be valid, reproducible, efficient, sensitive to
change in the underlying condition, and specific to the pathophysiology of
the condition. Few validated scales have been designed specifically for CIDP.
Those that have been used most frequently in clinical trials include generic
disability scores and a combination of objective functional assessments.8-11 These
scales are limited to an extent by their failure to account for the asymmetry
of CIDP in the generation of composite disability scores, by the potential
for interobserver and intraobserver bias and impaired reliability on testing-retesting,
and by the nonquantitative nature of describing functional impairment.
The Neuropathy Impairment Scale (previously called the Neurologic or Neuropathy Disability Score,
or NDS) or variations of this have been widely used to measure neurologic
deficit in CIDP as well as many other neuropathies.8, 12
It has been validated and has a high degree of reproducibility. It is, however,
a global score of muscle weakness and reflex and sensory abnormality; although
it is a good measure of global neuropathic abnormality, it is time consuming
and may lack sensitivity for detecting early asymmetric focal weakness indicative
of impending relapse and need for treatment as in our case.
More recently, the Inflammatory Neuropathy Cause and Treatment (INCAT)
Disability Scale11 was designed specifically
for neuropathy. The scores of this scale range from 0 to 5 each for upper
and lower limbs and are based on a combination of symptoms and functional
impairment. The overall score is based on the sum of disability in arm and
leg. Although specific for the pathophysiology, this scale has not been fully
validated, and the disability measurements may be subject to different interpretations
by different observers. Furthermore, the scale partially depends on defined
functional impairment, eg, symptoms of impairment in zipping and buttoning,
washing or brushing hair, using a knife and fork together, and handling small
coins, rather than on functions that may be of particular importance to the
individual patient. Moreover, the determination of whether an action is impaired
is to an extent subjective, which may limit the sensitivity of the test. Other
scales have attempted to address the symptomatic component of disability by
use of a rating system in which patients are examined with respect to a series
of defined tasks (eg, 9-hole peg test,13 maximal
grip strength, etc). However, such rating scales have not always been adequately
validated or objectively verified. For example, there is no correlation between
grip strength and performance in the 9-hole peg test14
in stroke patients, nor is there a correlation between muscle grip strength
and the ability to open a jar in a normal population.15
Furthermore, scales that are scored as "mild," "moderate," or "severe" are
limited by the risks of observer bias and should not be used as primary end
points, as different observers will define these measures differently.
Given the limitations of existing clinical rating scales for CIDP, we
sought to determine whether the observation of functional decline made by
a patient whose condition had been stabilized with IV immune globulin for
more than 5 years could be validated and used as an objective measure of early
decline and recovery of function. Our patient based her decision to seek repeat
infusions of IV immune globulin on the loss of her ability to operate her
aerosol deodorant. During the early years of her treatment, she had noted
that the decline in her ability to operate her deodorant was a reliable early
indicator of impending relapse, and that recovery of this function signaled
a general improvement in muscle strength. This specific functional impairment
was therefore used by the patient as a surrogate marker of her disease activity.
We sought to evaluate the reliability and validity of this observation, with
a view to developing an individually tailored scale that could be used in
the future to predict the efficacy of her treatment. We demonstrated that
objective measurement of strength required to operate the aerosol correlated
well with other accepted quantitative tests.
We have shown by this series of observations that it is possible to
objectively quantify a daily function nominated by a patient, such as operating
an aerosol can, and to subsequently use this function as a reliable indicator
of both decline and recovery in IV immune globulin–responsive demyelinating
neuropathy. That a subjective functional improvement can be directly translated
into an objective and reproducible test is important in the development of
clinical trials for patients with demyelinating neuropathy who are stable
with IV immune globulin therapy, and for whom it is desirable to explore the
efficacy of other non–blood-based therapeutic modalities. We submit
that such an approach, which is focused on functional loss as defined by the
patient and validated by test-retest and across control subjects, can be used
effectively to evaluate the efficacy of new treatments against the efficacy
of repeated infusions with IV immune globulin. We further submit that this
approach could be developed for more general use as a sensitive, valid, and
reliable scale for measurement of outcome in CIDP or to complement other scales.
AUTHOR INFORMATION
Accepted for publication February 13, 2002.
Author contributions: Study concept and design (Drs Pittock and Hardiman and Ms Meldrum); acquisition
of data (Dr Pittock and Ms Meldrum); analysis and
interpretation of data (Drs Pittock and Hardiman and Ms
Meldrum); drafting of the manuscript (Drs Pittock
and Hardiman); critical revision of the manuscript for important intellectual
content (Drs Pittock and Hardiman and Ms Meldrum);
statistical expertise (Dr Pittock and Ms Meldrum);
obtaining funding (Dr Hardiman); and administrative,
technical, or material support (Drs Pittock and Hardiman
and Ms Meldrum).
Corresponding author and reprints: Orla Hardiman, MD, FRCPI, Department
of Neurology, Beaumont Hospital, Beaumont Road, Dublin 9, Ireland (e-mail: ohard{at}iol.ie).
From the Departments of Neurology (Drs Pittock and Hardiman) and Physiotherapy
(Ms Meldrum), Beaumont Hospital, Dublin, Ireland. Dr Pittock is now with the
Department of Neurology, Mayo Clinic, Rochester, Minn. Ms Meldrum is now with
the Department of Physiotherapy, Royal College of Surgeons Ireland, Dublin.
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