Muscle Weakness- more than just a functional weakness/FTC consult!!!

We often get at least one consult every few days for "generalized weakness"...often we think about functional causes (i.e. deconditioning, anemia, etc). There are plenty of examples of muscle weakness with underlying diagnoses that we ought to be aware of an readily identify when assessing patients. Think broadly when approaching muscle weakess NYD! 

DDx- Muscle Weakness

-Inflammatory Myopathy: polymyositis, dermatomyositis, vasculitis, overlap syndromes (SLE, RA, Systemic Sclerosis, Sjogrens), critical illness neuromuscular disorders

-Infectious Myopathy: bacterial (lyme myositis, pyomyositis), viral (influenza, parainfluenza, HIV, CMV, Coxsackie, Echovirus, Adenovirus, EBV), Fungal, Parasitic (Trichinosis, toxoplasmosis)

-Drug/Toxic Myopathy: steroid, EtOH, cocaine, heroin, anti-malarial, statins, fibrates

-Endocrine Myopathy: hypothyroidism, hyperthyroidism, Cushings, DM, acromegaly

-Metabolic Myopathy: hypokalemia, hypocalcemia, hypophosphatemia, hyponatermia, hypernatremia, disorders of purine metabolism

-Neoplastic myopathy: paraneoplastic processes

-Rhabdomyolysis

• Drugs: EtOH, cocaine, statins, neuroleptic, malignant syndrome, malignant hyperthermia
• Hyperactivity: seizures, exertion (i.e. extreme exercise)
•  Trauma/operation: i.e. falls
•  Immobility

-Neurological

• Motor cortex: stroke, MS, brain tumor, abscess
• Corticospinal tract/Anterior Horn Cells: spinal cord injury, B12 deficiency, ALS, polio
•  Spinal nerve roots/peripheral nerves: GBS, Myeloma, amyloidosis, DM
• Neuromuscular junction: Myasthenia Gravis, botulism, organophosphate poisoning, Easton-Lambert
• Muscles: myopathies

Muscle Strength Grading

·       0=no contraction

·       1= flicker

·       2= possible only with gravity eliminated

·       3=against gravity only

·       4= power decreased but muscle contraction possible against resistance

·       5=normal power resistance

Investigations:

-Labs: CBC, Cr, urea, Albumin, Ca, Mg, PO4, albumin, CK, ESR, CRP, ALT, AST, ALP, GGT, ANA, ANCA, HBV/HCV serology, cryoglobulin, RF, TSH

-Special: EMG and NCS, muscle biopsy, PM/DM work-up (anti-Jo1, anti-SRP, anti-Mi2)