Ans. is 'd' i.e., Vitamin B12 Subacate combined degeneration of the spinal cord is the term used for the degeneration of the spinal cord due to vitamin Bp deficiency.o The spinal cord, brain, optic nerves, peripheral nerves mav all be affected in vitamin B.. deficiency but the spinal cord is usually affected first and exclusivelyThe tracts mainly involved in the spinal cord are:o Posterior columno Corticospinal tracto Later on peripheral nerves are involvedClinical features of vitamin B12 deficiency or subacute combined degeneration of the cord :o Patient first notices mild general weakenss and paresthesia consisting of tingling pins and needle.'o As the illness progresses the gait becomes unsteady and stiffness and weakenss of the limbs and legs develop. If the disease remains untreated ataxic paraplegia evolve.o Sometimes there may be loss of superficial sensations, such as tactile, pain and thermal sensations, but these signs are rare.o Loss of "vibration sense" is the most consistent sign and is usually accompanied by loss of position senseQ.o Motor signs seen are -Loss of strength in proximal limb musclesSpasticity, changes in tendon reflexesClonus and extensor plantar responsesSometimes tendon reflexes may be absent? (due to involvement of peripheral nerve)o Gait is ataxicNow,The Clinicopathological Correlation:Clinical featuresTracts involvedo Paresthesia, inpairment of deep sensation and ataxia-Due to lesion in posterior columno Weakness, spasticity and increased tendon reflexes-Due to corticospinal tract involvemento Occasional findings of toss of pain and temperature-Due to spinothalamic tract involvement (rarely involved)o Distal and symmetrical impairmeat of superficial sensation and loss of tendon reflexes-Involvement of peripheral nerve (occassionally)