<s>[INST] context: Tabes dorsalis is a feature of tertiary syphilis and is characterized by chronic fibrosing meningitis, which constricts the posterior root of the spinal cord. The posterior roots contain sensory nerves that originate in the spinal ganglia and form the posterior columns of the spinal cord. Compression of sensory nerves that originate in the posterior roots causes lancinating pain in extremities. It also damages the transmission of proprioceptive impulses, causing gait disturbances (ataxia). Amyotrophic lateral sclerosis (choice A) is a motor neuron disease that does not affect the posterior columns. Friedreich ataxia (choice B) is an autosomal dominant trait that involves the spinal cord in a complex way. It affects not only the centripetal pathways (spinocerebellar and posterior columns), but also the efferent corticospinal tracts. Subacute combined degeneration (choice E) is due to vitamin B12 deficiency and involves not only the posterior columns, but also the anterior horn cells and the spinocerebellar and corticospinal tracts.Diagnosis: Syphilis [/INST] question: A 50-year-old man presents with a "staggering" gait and "lightning pain" in his hands and legs. His past medical history is significant for an aortic aneurysm and aortic insufficiency. Neurologic examination reveals impaired senses of vibration, as well as touch and pain in the lower extremities. The patient subsequently dies of pneumonia. Autopsy discloses obliterative endarteritis of meningeal blood vessels and atrophy of the posterior columns of the spinal cord. What is the appropriate diagnosis? | options: A: Amyotrophic lateral sclerosis B: Friedreich ataxia C: Huntington disease D: Tabes dorsalis | answer: D </s>