LOWER MOTOR WEAKNESS:
1: PURE MOTOTR: (No sensory signs or symptoms at all):
It’s either motor neurone cell body disease or pure motor axonopathy.
Motor Neurone Cell Body Disease such as MND, Polio and Post-Polio Syndrome: Fasciculations means dying lower motor neurone’s cell bodies, so fasciculations can be seen in diseases affecting motor neurone cell bodies. Polio is acute onset and always asymmetrical, whereas MND is slow onset and symmetrical disease. Also MND can have upper motor signs too whereas polio never have upper motor signs. Cell bodies are within spinal cord, so CSF will not be affected.
Multifocal Motor Axonopathy: is an immune medicated damage to motor nerves. It’s mostly symmetrical & NCS will show pure motor axonopathy. It responds to steroids & immunosuppressive therapy.
2: PREDOMINATELY MOTOR (with some sensory symptoms &/or signs): Motor root disease such as GB syndrome or CIDP is mostly motor but patients often have sensory symptoms and sometimes signs too if sensory roots are also involved. CSF shows high proteins which are globulins with few or no Lymphocytes as roots are within CSF abs when immune system attacks roots by immunoglobulins it causes high CSF proteins. NCS will show delayed F-waves indicating issue at motor roots. CIDP, to simplify, can be considered as chronic form of GB syndrome (though it’s much different as it responds to steroids and etiology is different). Diabetes can also cause polyradiculopathy like GB, so always check for undiagnosed diabetes.
MIXED MOTOR & SENSORY:
It’s peripheral neuropathy as peripheral nerves has both sensory and motor fibres. Longer nerves (supplying feet are affected earlier than shorter nerves supplying hands). NCS will confirm it and CSF if done will be normal as nerves are outside the CSF (roots are in CSF).
Meningoradiculopathy due to chronic meningitis such as TB/syphilis/lyme’s/sarcoidosis etc can also present with mixed sensory motor signs etc due to roots being affected by chronic meningitis. CSF will have picture of chronic meningitis. Other clues for underlying maybe present too.
PREDOMINANTLY SENSORY: Could be due to predominantly sensory neuropathy OR dorsal root/dorsal root ganglion involvement. Dorsal root ganglion is often damaged by neurosyphilis etc. Sensory variant of GB can only or predominantly involve sensory roots.
NO MOTOR & NO SENSORY S/S:
Think of NMJ or Muscles. Reflexes should be intact and there should be no sensory or motor signs and symptoms.
NMJ such as Myaesthenia Gravis or LES syndrome.