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Pearls: Neuromuscular Disorders
Steven A. Greenberg, M.D.1
ABSTRACT
Various brief clinical observations helpful in the evaluation of patients with
neuromuscular disorders are discussed and illustrated. These include features of focal
neuropathies, including the neurologic thoracic outlet syndrome, apparent ulnar nerveinnervated hand weakness in radial neuropathies, scapula movement in long thoracic
compared with spinal accessory neuropathies, and diaphragm paralysis in segmental zoster
paresis. Potential diagnostic errors include multifocal motor neuropathy mistaken for nerve
tumor, the pseudoconduction block of vasculitic neuropathy leading to a diagnosis of
Guillain-Barré syndrome, and leg paralysis in myelopathy mistaken for early ascending
paralysis in Guillain-Barré syndrome. Very focal weakness of limb muscles occurs in
myasthenia gravis, similar to the more familiar focal cranial muscle involvement. Fluctuation, not fatigability, in myasthenia gravis is discussed. The presentation of Lambert-Eaton
myasthenic syndrome as a nonfluctuating subacute myopathy is emphasized. Patterns of
weakness in inclusion body myositis and facioscapulohumeral muscular dystrophy are
illustrated.
KEYWORDS: Thoracic outlet syndrome, Guillain-Barré syndrome, scapula, myasthenia
gravis, multifocal motor neuropathy
FOCAL NEUROPATHIES
Neurologic thoracic outlet syndrome
This syndrome has no relationship to the poorly
defined syndromes of arm pain, tingling, and subjective weakness that are often attributed to structures passing through the thoracic outlet, including
the brachial plexus. Rather, it is a slowly progressive
impairment in sensory and motor function of the
lower trunk or medial cord of the brachial plexus,
typically without pain (except for forearm or hand
muscle cramps) or symptoms varying with arm
position.1 Weakness of thenar and interossei muscles, often with relative sparing of abductor digiti
minimi, is characteristic. Magnetic resonance imaging (MRI) of the plexus is typically nondiagnostic;
1
Harvard Medical School, Department of Neurology, Brigham and
Women’s Hospital, Children’s Hospital Informatics Program, Boston,
Massachusetts.
Address for correspondence and reprint requests: Steven A.
Greenberg, M.D., Department of Neurology, Brigham and Women’s
Hospital, Children’s Hospital Informatics Program, 75 Francis Street,
Boston, MA 02115 (e-mail: [email protected]).
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rather, a chest anteroposterior (AP) lordotic or
cervical spine film should be considered, with attention specifically directed at the presence of an
enlarged C7 transverse process, sometimes articulating with a partial rib (Fig. 1).2 Consider this
diagnosis when there is both thenar and first dorsal
interosseous atrophy and medial hand and forearm
sensory disturbance.
Acute radial neuropathy
The sudden development of wrist and finger
extensor weakness that occurs in acute radial
neuropathies (for example, the ‘‘Saturday night
palsy’’) may be mistaken for an acute stroke or a
more proximal disorder, such as brachial plexopathy. This is because in addition to the obvious
Neurologic Pearls; Guest Editor, Stephen G. Reich, M.D.
Semin Neurol 2010;30:28–34. Copyright # 2010 by Thieme
Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001,
USA. Tel: +1(212) 584-4662.
DOI: http://dx.doi.org/10.1055/s-0029-1244992.
ISSN 0271-8235.
PEARLS: NEUROMUSCULAR DISORDERS/GREENBERG
Figure 1 Neurologic thoracic outlet syndrome. Atrophy of the right first dorsal interosseous and thenar muscles is seen in a
patient with bilateral C7 enlarged transverse processes (arrows) and ribs articulating off of these processes. (Reprinted with
permission from Greenberg SA. Neurologic thoracic outlet syndrome. Neurology 2002;59:E3.)
wrist and finger extensor weakness characteristic
of a radial nerve palsy, there is also what appears
to be ulnar-innervated hand weakness in the
finger abductors3 and, sometimes, elbow flexion
attributed to biceps weakness. The ‘‘pseudoulnar
weakness’’ is the result of the mechanical disadvantage of finger abductors when the fingers
are flexed compared with when they are extended. Elbow flexion weakness is due to involvement of the brachioradialis muscle. Test finger
adduction, such as adductor pollicis brevis, to
establish intact ulnar nerve function, and look at
the brachioradialis bulk by positioning both forearms at 90-degree angles at the elbows; then
rotate the forearms midway between full pronation and full supination, and ask the patient to
flex the arms against resistance, watching for the
visible decreased bulk in the brachioradialis on
the affected side as it contracts.
Scapular winging from focal neuropathy
Scapular winging may result from focal neuropathies affecting the long thoracic nerve, spinal
accessory nerve, or dorsal scapular nerve. Scapular
winging has also been reported uncommonly from
C7 radiculopathy.4 It may also be present in
generalized neuromuscular disorders, including
Figure 2 Distinct patterns of scapula winging. (A) Long thoracic neuropathy is shown with posterior and medial movement of
the scapula with forward flexion of the arm due to serratus anterior weakness. The middle and lower trapezius muscles
attempting to minimize the posterior displacement move the scapula medially; prominent contraction of the lower trapezius is
evident. (B) Partial spinal accessory neuropathy is seen in this patient’s back. Weakness of the middle trapezius, with sparing of
the upper trapezius, results in scapula movement that is lateral (from unopposed serratus anterior) and upward (from
unopposed upper trapezius) during arm abduction.
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2010
those of nerve (e.g., spinal muscular atrophy due to
PLEKHG5 mutations), neuromuscular junction
(e.g., COLQ mutations causing a congenital
myasthenic syndrome), or muscle (e.g., facioscapulohumeral muscular dystrophy).
The appearance of the scapula at rest and with arm
abduction and forward flexion differs between long
thoracic and spinal accessory neuropathies. In long
thoracic nerve lesions and serratus anterior weakness, such arm movements result in marked posterior displacement off the back, and medial
movement of the scapula as the unopposed middle
and lower trapezius muscles attempt to minimize
the posterior displacement (Fig. 2A).
Scapular winging from spinal accessory nerve
lesions results from weakness to the middle or
lower trapezius. The spinal accessory nerve supplies upper, middle, and lower trapezius; these
branches can be affected separately. Weakness of
the upper trapezius causes shoulder droop but not
scapular winging. Weakness of the middle or
lower trapezius produces winging that looks
very different from that of serratus anterior weakness. There is only slight posterior displacement
off the back; the scapula may move upward due
to the unopposed action of the upper trapezius,
and the lower border of the scapula moves laterally (Fig. 2B).
in the cervical myotomes, this may sometimes
produce asymptomatic unilateral diaphragm
paralysis.5 Consider obtaining chest radiographs
to look for unilateral hemidiaphragm elevation in
this setting (Fig. 3).
GENERALIZED NEUROPATHY
Multifocal motor neuropathy mistaken for nerve
tumor6
Multifocal motor neuropathy may initially be
mistaken for the presence of a nerve tumor on
MRI (Fig. 4) and result in an unnecessary nerve
biopsy. This mistake results when too much
attention is paid to the imaging studies, which
show a focal enlargement of the nerve with
similar signal changes to that of tumor, and
too little attention is given to the clinical presentation. Multifocal motor neuropathy may
present in a single nerve distribution as a motor
unit hyperactivity syndrome (cramps and fasciculations), a syndrome almost never seen with
nerve tumor, or as weakness without sensory
symptoms. Isolated peripheral nerve tumors
typically result in palpable paresthesias (sensory
symptoms after mechanical stimulation of the
region) and progressive sensory, more than
motor, impairment.
Segmental zoster paresis
Multifocal motor neuropathy treated with intravenous
In addition to the visible skin rash, herpes zoster
may also cause extramedullary sensory and motor
axon or intramedullary spinal cord injury. When
accompanied by segmental weakness, this syndrome
is called segmental zoster paresis. When occurring
immunoglobulin
The response of some patients with multifocal
motor neuropathy to treatment with intravenous
immunoglobulin is perhaps the most impressive
Figure 3 Segmental zoster paresis with unilateral hemidiaphragm paralysis. (Left) Rash. (Right) Elevated hemidiaphragm
(arrow).
PEARLS: NEUROMUSCULAR DISORDERS/GREENBERG
Figure 4 Multifocal motor neuropathy mistaken for nerve tumor on magnetic resonance imaging. Increased size and T2
signal intensity of the left radial nerve (arrows show enlargement of left compared with right radial nerves) in the mid-arm is
seen in a patient who presented with motor unit hyperactivity characteristic of multifocal motor neuropathy, but not
paresthesias or sensory disturbance characteristic of nerve tumor. Nerve biopsy had been planned for this patient because
of the radiological appearance, but was cancelled.
experience neuromuscular specialists have in the
course of their practice, and is sometimes of diagnostic value. Patients with decades of severe or
complete paralysis in a focal nerve distribution
may have partial recovery hours after the first single
intravenous immunoglobulin infusion and full recovery after several courses of treatment (Fig. 5).
‘‘Ascending paralysis’’ of Guillain-Barré syndrome
Guillain-Barré syndrome is often thought of as
an ascending paralysis. This phrase can be
misleading as most patients who seek medical
care with pronounced leg weakness, but no sensory or motor manifestations in the arms and
cranial nerves, do not subsequently have an ascending pattern due to Guillain-Barré; rather,
they have a myelopathy. It is important to consider immediately the possibility of a myelopathy
when such symptoms and signs are confined to
the legs.
Vasculitic neuropathy and pseudoconduction block
Sometimes aggressive vasculitic neuropathy is mistaken for Guillain-Barré syndrome.7,8 The rapidly
confluent involvement gives the impression of
a symmetric non-length-dependent neuropathy;
nerve conduction studies may be interpreted as
showing ‘‘conduction block,’’ a finding in this setting diagnostic of Guillain-Barré syndrome. However, acute nerve infarction studied within the first
few days to a week may also give findings typically
interpreted as conduction block, but whose nature is
Figure 5 Rapid response of long-standing paralysis due to multifocal motor neuropathy with intravenous immunoglobulin
treatment. (Left) Fifteen years of fixed weakness of specific finger flexors was rapidly reversed (right) hours after a first
intravenous immunoglobulin infusion.
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Figure 6 Pseudoconduction block in vasculitic neuropathy mistaken for conduction block in Guillain-Barré syndrome. Rapidly
progressive symmetric generalized weakness was suspected to be due to Guillain-Barré syndrome, and initial electrodiagnostic
studies (left) showed apparent conduction block, with drop in the amplitude of the left ulnar-abductor digiti minimi (ADM)
compound muscle action potential with forearm compared with wrist stimulation (right). Five days later, repeat electrodiagnostic
studies showed the distal-evoked compound muscle action potential had declined to the same amplitude as the forearm-evoked
potential because failure of neuromuscular transmission or axonal degeneration proceeded as a consequence of nerve infarct.
clarified by repeat studies a few days later as being
due to axonal injury. This is called ‘‘pseudoconduction block’’ (Fig. 6). Recognizing this initially takes
a high index of suspicion, with consideration of
the following: presence of fever (Guillain-Barré
syndrome is postinfectious and patients are rarely
febrile); history of multifocal involvement initially
that rapidly became confluent; asymmetric and focal
limb pain accompanying focal weakness; nerve conduction studies that show only ‘‘conduction block’’
but not focal slowing or temporal dispersion, other
features of demyelination.
Numbness in the hands before or at the same time as
the feet
The common distal symmetric polyneuropathies
are associated with sensory disturbances that start
in the toes and spread over time up the foot,
ankle, and lower leg. Often, the hands become
involved when leg numbness is in the mid or
upper lower leg (a pattern referred to as ‘‘lengthdependent’’). When numbness begins in the hands
and feet at the same time or close in time to each
other (a pattern often referred to as ‘‘non-lengthdependent’’), consider demyelinating neuropathy
or cervical myelopathy. Guillain-Barré syndrome
and chronic inflammatory demyelinating polyneuropathy often have this type of presentation
for sensory symptoms.
MUSCLE DISEASE
Finger flexor and quadriceps involvement in inclusion
body myositis
Inclusion body myositis is an often delayed diagnosis
that is frequently diagnosed as ‘‘refractory polymyositis’’ for several years before the correct diagnosis is
established. Substantial asymmetric weakness of
finger flexion (Fig. 7) and quadriceps muscles is a
distinctive pattern of inclusion body myositis, which
reliably distinguishes it from polymyositis.9,10 Comparing the deltoids with the finger flexors can be
especially helpful; the former is weaker in polymyositis, and the latter is weaker in inclusion body myositis.
Figure 7 Asymmetric finger flexor weakness for both
flexor digitorum superficialis (flexing proximal phalanges)
and flexor digitorum profundus (flexing distal phalanges) in
a patient with inclusion body myositis.
PEARLS: NEUROMUSCULAR DISORDERS/GREENBERG
Figure 8 Facioscapulohumeral muscular dystrophy. (A) Asymmetric bilateral pectoral muscle atrophy is seen with ‘‘axillary
crease’’ on the right side of the chest. (B) Beevor’s sign. (Left) Supine patient with head resting flat, note marker at the
umbilicus. (Right) with neck flexion, there is superior movement of the umbilicus.
Pattern of weakness in facioscapulohumeral muscular
NEUROMUSCULAR JUNCTION DISEASE
dystrophy
Focal limb weakness in myasthenia gravis
Weakness of facial (‘‘facio’’) muscles, winging
scapula (‘‘scapulo’’), and biceps (‘‘humeral’’) are
distinctive features of facioscapulohumeral muscular dystrophy (FSHD). The biceps and pectoral
(Fig. 8A, showing marked asymmetric pectoral
muscle atrophy) involvement is often substantial,
in contrast to relative sparing of the deltoid
(although shoulder abduction may appear weak
because of poor scapula fixation). Another physical
finding that has been emphasized is Beevor’s sign,
an upward movement of the umbilicus in a supine
patient flexing the neck (Fig. 8B), resulting from
lower abdominal muscle weakness.
Figure 9 Focal limb muscle weakness in myasthenia
gravis. Weakness of the right 5th digit extensor (arrowhead)
is seen.
Although neurologists are very familiar with focal
cranial musculature weakness in myasthenia gravis,
such as unilateral ptosis or unilateral superior rectus
weakness, similar focality in the limbs sometimes
raises concern regarding the diagnosis. It should not;
patients may have marked focal limb weakness, such
as: (a) isolated severe weakness of one triceps muscle
with all other arm muscles being normal bilaterally
or (b) one particular finger extensor weakened and
others not (Fig. 9).
Fatigable weakness in myasthenia gravis
An inability to sustain muscular force during physical
examination is often called ‘‘fatigable weakness’’ and
is considered a particularly helpful indicator of myasthenia gravis. However, almost all forms of motor
weakness involve a loss of the ability to sustain force;
this is seen in upper motor neuron disease, motor unit
disorders, and myopathy. A routine example includes
the pronator drift characteristic of upper motor
neuron lesions, although this sometimes has its origin
in sensory loss. What is more helpful than fatigability
during the course of a patient evaluation is fluctuation, which is marked by differing instantaneous
strength at different moments in time. An eyelid
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2010
include bilateral distal-evoked median and ulnar
compound muscle action potentials before and
after 10 seconds of exercise to detect facilitation
(Fig. 10).
REFERENCES
Figure 10 Postexercise facilitation in Lambert-Eaton
myasthenic syndrome. A small ulnar-abductor digiti minimi
(ADM) compound muscle action potential increases by 75%
after 10 seconds of exercise.
that is fully open at the beginning of an interview and
half closed later on, or vice versa, or a history of
substantial variation in motor symptoms at different
times is much more specific to myasthenia gravis.
Lack of fluctuating weakness in Lambert-Eaton myas-
thenic syndrome (LEMS):
Although LEMS is a disease of the neuromuscular
junction, many patients with LEMS do not
present with fluctuating weakness. Because many
neurologists have much more experience with
myasthenia gravis, they may be expecting fluctuation as a clue to LEMS. Rather, this syndrome
frequently presents more like a subacute myopathy, with progressive nonfluctuating leg and arm
weakness, and with dysautonomia.11 Consider
LEMS in any patient with such a subacute myopathy, and ask for electrodiagnostic studies that
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