A 67-year-old man is brought to the office by his wife due to a month of increasing forgetfulness. Over the last 2 weeks, she has noticed that his gait has been unsteady. The patient reports increased fatigue. He has hypertension and hyperlipidemia, and is compliant with all medications. Over the last month, the patient has taken over-the-counter stool softeners for constipation. He worked as an automobile mechanic for 30 years before retiring last year. The patient smokes a pack of cigarettes daily and usually has a beer after dinner, but recently started drinking home-distilled whiskey. Blood pressure is 120/80 mm Hg, and pulse is 76/min. Examination shows clear lung fields and normal first and second heart sounds. The abdomen is soft and nontender without organomegaly. There is weakness on dorsiflexion of bilateral wrists and feet. Pinprick sensation is reduced over the hands and feet. Upper and lower limb deep tendon reflexes are 1+. Laboratory results are as follows: Which of the following underlying mechanisms is most likely associated with this patient's clinical presentation?

Question

A 67-year-old man is brought to the office by his wife due to a month of increasing forgetfulness.  Over the last 2 weeks, she has noticed that his gait has been unsteady.  The patient reports increased fatigue.  He has hypertension and hyperlipidemia, and is compliant with all medications.  Over the last month, the patient has taken over-the-counter stool softeners for constipation.  He worked as an automobile mechanic for 30 years before retiring last year.  The patient smokes a pack of cigarettes daily and usually has a beer after dinner, but recently started drinking home-distilled whiskey.  Blood pressure is 120/80 mm Hg, and pulse is 76/min.  Examination shows clear lung fields and normal first and second heart sounds.  The abdomen is soft and nontender without organomegaly.  There is weakness on dorsiflexion of bilateral wrists and feet.  Pinprick sensation is reduced over the hands and feet.  Upper and lower limb deep tendon reflexes are 1+.  Laboratory results are as follows:  Which of the following underlying mechanisms is most likely associated with this patient's clinical presentation?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d495_647f_bc81_9bf3005434f3_MD0003_00 This patient's presentation suggests acute lead toxicity, which can include: Gastrointestinal manifestations (eg, abdominal pain, constipation) Neuropsychiatric manifestations (eg, forgetfulness), motor and sensory neuropathies (eg, extensor weakness, stocking-glove distribution) Hematologic manifestations (eg, microcytic anemia) Nonspecific symptoms (eg, fatigue, irritability, insomnia) are common. Chronic lead exposure can also cause hypertension and nephropathy. Diagnosis hinges on eliciting a history of exposure through occupation (eg, battery manufacturing, plumbing, home restoration) or other means (eg, distillation of alcohol through parts with lead soldering). Lead is primarily absorbed via the respiratory tract in adults but may otherwise be absorbed through the skin or gastrointestinal tract. It is 99% bound to erythrocytes and can disrupt heme synthesis to cause microcytic anemia. Diagnosis is made via blood lead levels, complete blood count with blood smear, and x-ray fluorescence to measure bone lead concentration. Peripheral blood smear can show basophilic stippling. Hyperuricemia (due to impaired purine metabolism) is also typical. basophilic stippling (Choices A and B) Cerebral amyloid deposition is the pathogenic mechanism of Alzheimer disease. It is associated with impairment of memory and executive function and insidious neuropsychiatric disturbances but with an otherwise normal gait and neurological examination, especially in the early stages. Neuronal degeneration in the substantia nigra is responsible for Parkinson disease, characterized by bradykinesia, resting "pill-rolling" tremor, rigidity, shuffling gait, and postural instability. Neither is usually associated with peripheral neuropathy, hyperuricemia, or microcytic anemia. (Choices C and D) Thiamine (vitamin B₁) deficiency is seen with alcohol abuse or white-rice/cereal-based diets and manifests as Wernicke-Korsakoff syndrome (eg, nystagmus, ophthalmoplegia, ataxia, confabulation) or beriberi (eg, distal and symmetric peripheral neuropathy, cardiomyopathy). Cobalamin (vitamin B₁₂) deficiency (from pernicious anemia, gastrectomy, or intestinal malabsorption) leads to macrocytic anemia and subacute combined degeneration (eg, spasticity, incontinence, paraplegia). Neither deficiency is usually associated with microcytic anemia or hyperuricemia. ₁ ₁₂ (Choice F) Diabetes leads to glycosylation of many end-products, increasing the risk of cardiovascular disease, nephropathy, retinopathy, and neuropathy (eg, peripheral neuropathy, gastroparesis). It typically does not cause prominent forgetfulness, gait unsteadiness, microcytic anemia, or hyperuricemia. (Choice G) Recurrent lacunar basal ganglia infarcts lead to subcortical vascular dementia, which can cause gait disturbance, unsteadiness, and mild memory impairment. However, it is often characterized by a stepwise decline with focal motor deficits and sometimes personality changes. Educational objective: Lead toxicity is usually due to lead exposure at work or home. Patients may present with nonspecific (eg, fatigue, irritability, insomnia), neuropsychiatric (eg, neurocognitive deficits, peripheral neuropathy), or gastrointestinal manifestations. References: Clinical, toxicological, biochemical, and hematologic parameters in lead exposed workers of a car battery industry. (http://www.ncbi.nlm.nih.gov/pubmed/23645955) Buyers beware: lead poisoning due to Ayurvedic medicine. (http://www.ncbi.nlm.nih.gov/pubmed/22476953)

A 67-Year-Old Man Is Brought to the Office by His