Weakness

Basics

Defined as a decrease in physical strength or energy
Patients will use “weakness” to describe many different symptoms and presentations
May represent neuromuscular weakness, fatigue, malaise, presyncope, or other symptoms
History and physical is key to help narrow diagnosis and workup
Often multifactorial
Distinguish neuromuscular disorder/focal neurologic process vs. nonneuromuscular disorder
Distinguish focal weakness vs. bilateral or generalized weakness
Categories of neuromuscular disorders:
- Upper motor neuron (UMN) lesions:
  - Deep tendon reflexes (DTR) increased
  - Plantar reflexes upgoing
  - Increased muscle tone
  - Muscle atrophy absent
- Lower motor neuron (LMN) lesions:
  - DTRs decreased to absent
  - Plantar reflexes absent or normal
  - Decreased muscle tone
  - Muscle atrophy present
  - Fasciculations
- Neuromuscular junction (NMJ) lesions:
  - DTRs normal
  - Plantar reflexes normal or absent
  - Decreased muscle tone
Categories of nonneuromuscular disorders:
- Neurologic
- Infectious
- Traumatic/structural
- Endocrine
- Metabolic
- Cardiac
- Rheumatologic
- Toxicologic
- Other
- Psychiatric

Neuromuscular disorders:
- Multiple sclerosis (UMN)
- Amyotrophic lateral sclerosis (mixed)
- Transverse myelitis (UMN)
- Guillain–Barré syndrome (LMN)
- Myasthenia gravis (NMJ)
- Lambert–Eaton syndrome (NMJ)
- Periodic paralysis (can be familial)
Neurologic:
- TIA/CVA
- Seizure (Todd paralysis)
- Malignancy
Infection/sepsis:
- UTI
- Pneumonia
- Meningitis
- Mononucleosis
- HIV
- Arboviruses
- Botulism (NMJ)
- Diphtheria
- Epidural abscess (often seen with IV drug use)
- Poliomyelitis
Traumatic/structural:
- Intracranial hemorrhage
- Spinal cord injury/lesion
- Malignancy
- Cauda equina
- Impingement syndromes
Endocrine:
- Hypothyroidism
- Adrenal crisis
- Vitamin deficiency
Metabolic:
- Dehydration
- Hypoglycemia
- Electrolyte abnormalities
Cardiac:
- Myocardial ischemia
- Arrhythmia
- Presyncope
Rheumatologic:
- Systemic lupus erythematosus
- Polymyalgia rheumatica
- Myositis
Toxicologic:
- Seafood toxins
- Tick paralysis (NMJ)
- Carbon monoxide poisoning
- Heavy metal poisoning
- Drugs of abuse
- Alcohol
- Organophosphates and carbamates (history of pesticide exposure)
Anemia
Pregnancy
Psychiatric causes of weakness (diagnoses of exclusion):
- Anxiety/depression
- Dependent personality
- Hypochondriasis
- Chronic fatigue syndrome
- Fibromyalgia
- Malingering

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