A 65-year-old man comes to the office due to recurrent falls. For the last several months, the patient has had a sensation of imbalance that is worse at night but has no associated pain or motor weakness. Medical history is notable for type 2 diabetes mellitus diagnosed 20 years ago and hypertension diagnosed 10 years ago. The patient was found to have nonproliferative diabetic retinopathy at his last ophthalmologic visit. Current medications include insulin, metformin, rosuvastatin, and ramipril. He does not use tobacco but drinks 1 or 2 beers daily and, often, more on weekends. Physical examination shows decreased proprioception and vibration sense in the feet. Ankle jerk reflexes are absent. Finger-to-nose and heel-to-shin tests are normal, but the patient sways and tends to fall when his eyes are closed. Bilateral hammer toe deformities are present. The remainder of the examination is unremarkable. Which of the following processes is predominantly responsible for this patient's neurologic symptoms?

Question

A 65-year-old man comes to the office due to recurrent falls.  For the last several months, the patient has had a sensation of imbalance that is worse at night but has no associated pain or motor weakness.  Medical history is notable for type 2 diabetes mellitus diagnosed 20 years ago and hypertension diagnosed 10 years ago.  The patient was found to have nonproliferative diabetic retinopathy at his last ophthalmologic visit.  Current medications include insulin, metformin, rosuvastatin, and ramipril.  He does not use tobacco but drinks 1 or 2 beers daily and, often, more on weekends.  Physical examination shows decreased proprioception and vibration sense in the feet.  Ankle jerk reflexes are absent.  Finger-to-nose and heel-to-shin tests are normal, but the patient sways and tends to fall when his eyes are closed.  Bilateral hammer toe deformities are present.  The remainder of the examination is unremarkable.  Which of the following processes is predominantly responsible for this patient's neurologic symptoms?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d256_2338_bc81_a5207853a7ff_MD0003_00 Diabetes mellitus is the most common cause of peripheral neuropathy, with the risk related to the duration of the disease and glycemic status. Neuronal injury in diabetes is due to a number of factors, including microvascular injury, demyelination, oxidative stress, and deposition of glycation end products. The use of metformin, which decreases intestinal absorption of vitamin B₁₂, can also contribute. This leads to a length-dependent axonopathy, with clinical features occurring first in the longest nerves (eg, feet). ₁₂ Symmetric distal sensorimotor polyneuropathy is the most common neuropathy in patients with diabetes; the clinical features depend on the type of nerve fibers involved. Small fiber injury is characterized by the predominance of positive symptoms (eg, pain, paresthesia, allodynia) (Choice B). Large fiber involvement is characterized by the predominance of negative symptoms (eg, numbness, loss of proprioception and vibration sense, diminished ankle reflexes). This patient primarily has features of large fiber involvement, with loss of position sense causing gait imbalance (worsened with eye closure due to lack of visual compensation) and weakness of the intrinsic muscles of the feet leading to foot deformities (eg, hammer toe deformity). (Choice C) Degeneration of the cerebellar hemispheres (eg, due to alcohol use) can cause gait disturbances due to incoordination of the limbs. However, most patients have additional abnormalities, including dysmetria (eg, abnormal finger-to-nose test), dysarthric speech, and intention tremor. (Choice D) Proprioception and vibration sense are carried by the posterior column of the spinal cord, and lesions there may resemble large fiber neuropathy. In contrast, the anterolateral system (eg, lateral spinothalamic tract) carries primarily pain and temperature sensation. (Choice E) Patchy demyelination may occur in diabetic neuropathy. Diffuse demyelination is seen in Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy and is usually associated with more severe motor weakness. Educational objective: Sensorimotor polyneuropathy in diabetes is characterized by length-dependent axonopathy. Small fiber involvement causes pain, paresthesia, and allodynia, whereas large fiber injury causes numbness, loss of proprioception and vibration sense, and diminished ankle reflexes. References: Physiology in medicine: neuromuscular consequences of diabetic neuropathy. (http://www.ncbi.nlm.nih.gov/pubmed/26989220)

A 65-Year-Old Man Comes to the Office Due to Recurrent