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Muscle Weakness
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Muscle Weakness
, Generalized Muscle Weakness, Bilateral Muscle Weakness
See Also
Muscle Weakness Causes
Muscle Weakness in Children
Acute Motor Weakness Causes
(
Emergent Bilateral Motor Weakness
)
Acute Flaccid Paralysis
Medication Causes of Myositis
Unilateral Weakness
Myopathy
Neuropathy
Fatigue
Dyspnea
Arthralgia
Epidemiology
Weakness affects 5% of adults oiver age 60 years old
History
Onset
Acute onset within hours to days should prompt urgent assessment
See
Acute Motor Weakness Causes
(
Emergent Bilateral Motor Weakness
)
Acute
Unilateral Weakness
(aside from focal weakness) should prompt emergent
CVA Evaluation
Distinguish weakness from
Fatigue
and
Asthenia
Asthenia
is exhaustion without weakness
Fatigue
is inability to perform task repeatedly
Weakness is inability to perform task initially
Consider
Frailty
and
Sarcopenia
of advanced age
Distinguish weakness from pain-related disuse (e.g. specific joint
Osteoarthritis
)
Determine distribution
Unilateral Weakness
(typically neurologic, especially if sensory involvement)
Cerebrovascular Accident
(CVA, critical to exclude in acute cases)
Mononeuropathy
(
Focal Peripheral Neuropathy
)
Multiple Sclerosis
Myasthenia Gravis
Symmetric proximal weakness (e.g. rising from chair, climbing steps, raising arms overhead)
Myopathy
See
Myopathy Causes
(e.g.
Polymyositis
,
Polymyalgia Rheumatica
,
Thyroid
disease)
Symmetric distal weakness (e.g. drops items, cannot open jars, foot drop)
Polyneuropathy
Guillain-Barre Syndrome
(affects proximal muscles as well)
Amyotrophic Lateral Sclerosis
Myopathy
less commonly effects distal muscles
Statin
s,
Alcohol
may effect distal and proximal
Inclusion body
Myositis
Myotonic dystrophy
Contributing factors
Medication history
See
Medication Causes of Myositis
Substance use history
Alcohol Abuse
Cocaine Abuse
Huffing
(esp. Glue)
Family History
Gene
tic
Muscular Dystrophy
Disorders of metabolism
Exam
Neurologic Exam
Motor Strength
Evaluate specific upper and lower extremity testing (e.g. ulnar, median and
Radial Nerve
function)
Evaluate for symmetric versus asymmetric weakness
Upper Motor Neuron Lesion
(everything is UP - tone, reflexes, toes)
Lower Motor Neuron Lesion
(everything is DOWN - tone, reflexes, toes)
Sensory Exam
Evaluate for dermatomal distribution of sensory loss
Deep Tendon Reflex
es
Hyperreflexia (
Upper Motor Neuron Lesion
,
Hyperthyroidism
,
Hypercalcemia
)
Hyporeflexia (
Lower Motor Neuron Lesion
,
Hypothyroidism
)
Cranial Nerve
Exam
Ptosis
and
Diplopia
may suggest
Myasthenia Gravis
Evaluate for
Sarcopenia
and
Frailty
Grip strength
Get Up and Go Test
Exam
Gene
ral
Dermatomyositis
changes (e.g. heliotrope rash, gottron
Papule
s)
Cushing's Disease
changes (
Obesity
,
Hypertension
,
Hirsutism
, abdominal striae)
Thyroid
changes (e.g.
Goiter
)
Evaluation
Is motor weakness NOT objectively identified on exam?
Conside
Asthenia
(exhaustion without weakness)
Consider
Fatigue
(inability to perform task repeatedly)
Consider
Frailty
and
Sarcopenia
of advanced age
Consider
Dyspnea
Upper Motor Neuron Lesion
(muscle group weakness without atrophy, hyperreflexia)?
Acute Onset
Emergency evaluation for
Cerebrovascular Accident
head imaging
Subacute Onset
Evaluate with head imaging for
CNS Lesion
,
Spinal Cord Syndrome
,
Multiple Sclerosis
Upper Motor Neuron Lesion
AND
Lower Motor Neuron Lesion
Evaluate for
Amyotrophic Lateral Sclerosis
(Neurology,
Electromyogram
,
Nerve Conduction Studies
)
Lower Motor Neuron Lesion
(
Flaccid Paralysis
with muscle atrophy, fasciculations and hyporeflexia) OR non-specific
Weakness is affected by repetition
Weakness worsens with repetition:
Myasthenia Gravis
(associated with
Ptosis
,
Diplopia
,
Dysarthria
,
Dysphagia
)
Anti-acetylcholine receptor
Antibody
positive
Neurology
Consultation
and (if labs negative,
Electromyogram
,
Nerve Conduction Studies
)
Weakness improves with repetition:
Lambert-Eaton Syndrome
Voltage-Gated Calcium Channel
Antibody
positive
Neurology
Consultation
and (if labs negative,
Electromyogram
,
Nerve Conduction Studies
)
Sensory deficit
Suggests
Neuropathy
(e.g.
Diabetic Neuropathy
)
Evaluate with
Serum Glucose
,
Vitamin B12
Evaluate for
Substance Abuse
and toxin exposures
Consider Neurology
Consultation
and
Electromyogram
,
Nerve Conduction Studies
Muscle biopsy may be considered in unclear cases
Asymmetric weakness
Consider
Compressive Neuropathy
, Parsonage-
Turner Syndrome
Consider Neurology
Consultation
and
Electromyogram
,
Nerve Conduction Studies
Consider MRI Brain
Symmetric weakness
Painful
Consider
Medication Causes of Myositis
(esp.
Statin
s and
Quinolone
s)
Consider
Rhabdomyolysis
and inflammatory
Myopathy
Evaluate with CK, myoglobin, ESR, CRP and consider ANA
Consider Rheumatology
Consultation
Consider Neurology
Consultation
Muscle biopsy may be considered in unclear cases
Not significantly painful
See
Muscle Weakness Causes
Broad-based laboratory evaluation (e.g. chem8, TSH, CK, cortisol)
Careful history including
Substance Abuse
, toxin exposures and
Family History
Consider Neurology
Consultation
and
Electromyogram
,
Nerve Conduction Studies
Muscle biopsy may be considered in unclear cases
Differential Diagnosis
See
Muscle Weakness Causes
See
Acute Motor Weakness Causes
(
Emergent Bilateral Motor Weakness
)
Consider
Frailty
and
Sarcopenia
of advanced age
Consider primary neurologic disorders
See
Neuropathy
Upper Motor Neuron Lesion
(e.g. CVA,
Multiple Sclerosis
)
Lower Motor Neuron Lesion
(e.g.
Guillain-Barre Syndrome
,
Compressive Neuropathy
)
Consider primary muscle disorders
Myotonia (muscle stiffness)
Myositis
(e.g.
Polymyositis
,
Dermatomyositis
, Inclusion body
Myositis
)
Muscular Dystrophy
(e.g. Becker
Muscular Dystrophy
, Limb-Girdle
Muscular Dystrophy
, Myotonic Dystrophy)
Consider toxic and metabolic causes
See
Toxic Myopathy
(
Medication Causes of Myositis
)
Electrolyte
disturbance (e.g.
Hypokalemia
)
Endocrine disorder (e.g.
Hyperthyroidism
or
Hypothyroidism
)
Labs
As Indicated
See
Neuropathy
Myopathy
(see also
Polymyositis
)
Creatine Kinase
(CPK)
Erythrocyte Sedimentation Rate
C-Reactive Protein
Serum chemistry (e.g. Chem 8)
Electrolyte
s
Glucose
, calcium,
Magnesium
, phosphate
Thyroid Stimulating Hormone
(TSH)
Urinalysis
Myoglobinuria
Vitamin B12
Other tests as indicated
24-hour urine cortisol
Growth Hormone
Antinuclear Antibody
HIV Test
Lyme Disease Test
West Nile Virus
Test
Dengue Fever
Test
Lumbar Puncture
Anti-acetylcholine receptor
Antibody
(
Myasthenia Gravis
)
Weakness improves with repetition:
Imaging
As Indicated
MRI Brain
Diagnostics
As Indicated
Electromyogram
Nerve Conduction Studies
Muscle Biopsy
Reserved for specific
Myopathy
cases (objective weakness and positive testing), typically by neurology recommendation
Biopsy performed by surgical consultant of muscle with mild to moderate weakness
Avoid biopsy of muscles with severe weakness (nondiagnostic results with fat and fibrosis change)
References
Nayak (2017) Worl J Clin Cases 5(7): 270-9
https://www.wjgnet.com/2307-8960/full/v5/i7/270.htm
Chawla (2011) Front Neurol 2:49 +PMID:21886637 [PubMed]
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3153853/
Larson (2020) Am Fam Physician 101(2):95-108 [PubMed]
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