<prompt> All are causes of spastic paraplegia except:Subacute combined degenerationMotor neuron diseaseAcute demyelinating encephalopathyFluorosis  <response>: Ans: d FluorosisRef: Harrison, 17 ed. pg. 2595 Adam Victor NeurologySACD B defeciency Subacute paraesthesia in hand feet, spatic paraparesis, loss of posterior column sensations, optic atrophy, irritabilitymental changes.Causes loss of ankle jerk with extensor plantar.Motor neuron disease Usually presents as insidious onset assymetric weakness of distally in one of the limbs. Progressive wasting and atrophy of the muscles with fasciculations Exaggerated DTR with spastic weakness of the limbs in predominant corticospinal involvement Spares cognitive functions, bowel bladder, sensory system and ocular motility till late stages.ADEM: Clinical featuresEncephalitic form - fever, headache, confusion, convulsions, coma, decerebrate rigidity.Myelitic form -Partial or complete paraplegiaquadriplegiawith varying degree of bowel bladder involvement.Flurosis: Even though there are case reports about fluorosis presenting as spastic paraparesis due to involvement of the spine it is very rare and hence the most possible answer here. 