AM Report Pearls: Systematic Approach to Weakness

AM Report Pearls: Systematic Approach to Weakness

Step 1: Distinguish true muscle weakness vs perceived weakness

Causes of functional/perceived weakness:

  • Deconditioning/Muscle wasting from prolonged bedrest – on exam, you can see symmetric weakness in all extremities, no decreased reflexes or focal neuro deficits
  • Functional/psychogenic weakness – on exam, you can do maneuvers to distinguish between true weakness and psychogenic – note that this is a diagnosis of exclusion!

Step 2: Localize the lesion! CNS Lesion or PNS Lesion? Physical Exam helps you distinguish!

CNS Causes of Weakness:

  1. Brain – on exam, usually ASYMMETRIC neuro findings, look for UMN signs (hyperreflexia, spasticity, Babinski) and cortical signs (language, neglect, field cuts)
    • Strokes
    • Space-occupying lesions/masses
  2. Spinal cord – on exam, can be asymmetric OR symmetric neuro findings, look again for UMN signs
    • Demyelinating disease (like MS)
    • Infection (epidural abscess, discitis/osteomyelitis)
    • Malignancy (mets to the spinal cord – commonly seen in Breast cancer, prostate cancer or primary spine malignancies like multiple myeloma)
    • Vascular abnormalities i.e. spinal infarction (often seen post-operatively)
    • Post-traumatic spinal cord injury

PNS Causes of Weakness

  1. Peripheral nerve – can be asymmetric or symmetric – check for LMN signs (hyporeflexia, decreased muscle bulk/tone, atrophy, fasiculations)
    • Symmetric polyneuropathies à Think of DM (most common), toxic (ETOH), metabolic (B12 deficiency, copper deficiency that mimics B12 deficiency)
    • Mononeuropathy à Think of mononeuritis multiplex (seen in DM or vasculitis), think of nerve compression (e.g. carpal tunnel, tarsal tunnel)
  2. Neuro-muscular junction: usually symmetric, usually proximal muscle weakness, check for bulbar signs/symptoms (the “D” symptoms – dysphagia, dysphonia, dysarthria)
    • Myesthenia Gravis à note fatiguability with repeated movements
    • Lambert-Eaton (paraneoplastic) à facilitation with repeated movements
    • In SF, don’t exclude botulism from IVDU!
  3. Muscle i.e. Myopathy: often symmetric, tends to be proximal > distal
    • Medications (e.g. statins)
    • Substance abuse particularly alcohol
    • Endocrinopathies (hyper or hypothyroidism, Cushing’s disease)
    • Autoimmune (dermatomyositis, polymyositis)

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