Thanks to Evie for presenting! Today we had an excellent case about a young patient coming in with acute-subacute symmetric bilateral proximal muscle weakness and paresthesias after a recent URI found to have most likely a viral myositis.
A few learning points:
1) The differential diagnosis for weakness can be broken down into 4 main groups: CNS, PNS/neuromuscular, oxygen delivery, and other.
2) Early UMN lesions may present with hyporeflexia.
3) EMG is a great modality to use to help sort out the differential for neuromuscular conditions. It can be used to localize the lesion [anterior horn vs nerve (root or axonal or demyelinating) vs NMJ vs muscle] as well as determine chronicity.
Want to know more?
- a. CNS lesions
- b. Spinal cord – MS/TM/ADEM, epidural compression, vascular
- a. Anterior horn – ALS is the classic (also polio, west nile, lead)
- b. Peripheral nerve
- i. mononeuropathy & plexopathy eg. carpal tunnel
- ii. mononeuritis multiplex eg. vasculitis
- iii. polyneuropathy
- axonal eg. DM (also B12, thyroid, toxins, infectious, vasculitis, paraproteinemic)
- demyelinating eg. AIDP (GBS)/ CIDP (also CMT)
- c. NMJ – Myesthenia gravis, Lambert-Eaton are classic (also west nile)
- d. Muscle/ myopathy – can be separated into inflammatory (eg DM/PM), infectious, endocrine, toxic, metabolic/electrolytes, paraneoplastic, critical illness
3) Oxygen delivery
- a. Remember DO2 = CO x Hgb x O2 sat so this would include cardiovascular, pulmonary, anemia etc.
- a. Psych
Localization of PNS lesions: Here is a great PDF created by former UCSF chiefs that breaks down using the exam and EMG to determine etiology.
Transverse myelitis: An illness script for transverse myelitis is a young patient coming in with acute-subacute symmetric motor, sensory and autonomic dysfunction usually with a clearly defined sensory level. Etiologies include 1) idiopathic 2) infectious or inflammatory 3) toxic-metabolic and 4) MS-NMO related condition. The usual workup includes MRI w gadolinium contrast and LP (looking for CSF pleocytosis or elevated IgG index). Brain imaging, and visual evoked potentials are needed to distinguish TM from MS-NMO-ADEM. The TM consortium workgroup has a nice paper about this.
Viral myositis: An illness script for viral myositis is a person coming in with a recent viral prodrome (days-2 weeks) found to have elevated CK. Some culprits include: flu, coxsackie, EBV, HSV, paraflu, adeno, echo, CMV, measles, VZV, HIV, and dengue.