II. Epidemiology
- Weakness affects 5% of adults oiver age 60 years old
III. 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
- Acute onset within hours to days should prompt urgent assessment
- 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)
- Myopathy
- 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
- Statins, Alcohol may effect distal and proximal
- Inclusion body Myositis
- Myotonic Dystrophy
- Unilateral Weakness (typically neurologic, especially if sensory involvement)
- Contributing factors
- Medication history
- Substance use history
- Alcohol Abuse
- Cocaine Abuse
- Huffing (esp. Glue)
- Family History
- Genetic Muscular Dystrophy
- Disorders of metabolism
IV. 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 Reflexes
- 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
V. Exam: General
- Dermatomyositis changes (e.g. heliotrope rash, Gottron Papules)
- Cushing's Disease changes (Obesity, Hypertension, Hirsutism, abdominal striae)
- Thyroid changes (e.g. Goiter)
VI. 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
- Acute Onset
-
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)
- Weakness worsens with repetition: Myasthenia Gravis (associated with Ptosis, Diplopia, Dysarthria, Dysphagia)
- 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. Statins and Quinolones)
- 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
- Painful
- Weakness is affected by repetition
VII. 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
- 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)
VIII. Labs: As Indicated
- See Neuropathy
-
Myopathy and Differential Diagnosis (see also Polymyositis)
- Complete Blood Count
- Comprehensive Metabolic Panel (e.g. Chem 18)
- Electrolytes Glucose, Calcium, Magnesium, phosphate
- Liver Function Tests (AST, ALT)
- Creatine Kinase (CPK)
- Erythrocyte Sedimentation Rate
- C-Reactive Protein
- Thyroid Stimulating Hormone (TSH)
- Urinalysis
- Serum Vitamin B12
- Other tests as indicated
- Endocrine testing
- 24-hour urine Cortisol
- Growth Hormone
- Celiac Serology
- B-Hexaminidase Subunit alpha and beta activity (Ashkenazi jewish descent, risk for Tay Sachs)
- Viral testing
- Lumbar Puncture (CSF)
- CSF Cell Count and Differential
- CSF Protein
- CSF Glucose
- Oligoclonal Bands
- Autoimmune testing
- Toxicology
- Consider Heavy Metal testing if known exposures (e.g. Lead Poisoning, Mercury Poisoning)
- Endocrine testing
IX. Imaging: As Indicated
- MRI Brain
- Spine MRI