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Difficulty: HardMedical History Evaluation

A 62-year-old man presents to the outpatient clinic with a 6-month history of progressive difficulty walking and tingling in his feet. He describes his legs as feeling 'stiff and heavy.' He also reports increased fatigue over the same period. His past medical history includes hypertension, benign prostatic hyperplasia, and complete edentulism. He takes amlodipine and tamsulosin. He does not use tobacco, alcohol, or illicit substances. Neurological examination reveals a spastic, wide-based gait, bilateral lower extremity hyperreflexia, positive Babinski signs, and markedly decreased vibratory and position sense in the toes. Laboratory studies reveal a hemoglobin of 9.2 g/dL9.2 \text{ g/dL} with a mean corpuscular volume of 74 fL74 \text{ fL}, and an absolute neutrophil count of 900/mm3900/\text{mm}^3. Serum vitamin B12, folate, and methylmalonic acid levels are within normal limits. Which of the following questions during the medical history evaluation is most likely to reveal the etiology of this patient's condition?

  1. A
    Have you noticed any dark, tarry stools or blood in your bowel movements?
  2. B
    Have you recently experienced increased thirst, frequent urination, or blurred vision?
  3. How frequently and in what quantity do you apply denture adhesive?Answer
  4. D
    Are you taking any over-the-counter proton pump inhibitors for heartburn?
  5. E
    When was your last screening colonoscopy for colorectal cancer?

Answer

The correct approach is to inquire about the frequency and quantity of denture adhesive use, as excessive use of zinc-containing adhesives can lead to zinc toxicity and subsequent copper deficiency.
This patient presents with a classic triad for copper deficiency: a myeloneuropathy indistinguishable from subacute combined degeneration (dorsal column and corticospinal tract involvement), microcytic anemia, and neutropenia. Because his vitamin B12 and methylmalonic acid levels are normal, B12 deficiency is definitively excluded. A well-documented cause of acquired copper deficiency is zinc toxicity. High levels of exogenous zinc stimulate the synthesis of metallothionein within intestinal enterocytes. Metallothionein has a substantially higher affinity for copper than for zinc; thus, dietary copper becomes trapped within the enterocytes and is lost when these cells naturally slough into the fecal stream. A classic historical clue for this condition is the excessive use of zinc-containing denture adhesives, which is highly relevant given this patient's complete edentulism. Asking about denture adhesive use is the critical next step in evaluating his medical history to secure the diagnosis.

Step-by-Step Solution

1
Analyze the neurological presentation.
The patient has upper motor neuron signs (hyperreflexia, Babinski) and posterior column signs (decreased vibratory/position sense), indicating a myeloneuropathy identical to subacute combined degeneration.
Identifying the specific pattern of neurological deficits localizes the lesion and narrows the differential diagnosis.
2
Integrate the laboratory findings.
The presence of microcytic anemia and neutropenia, coupled with normal B12 and methylmalonic acid levels, rules out Vitamin B12 deficiency.
B12 deficiency typically presents with macrocytic anemia. The specific combination of myeloneuropathy, microcytic anemia, and neutropenia points directly to copper deficiency.
3
Connect the clinical clue to the underlying etiology.
The patient's complete edentulism suggests the use of dentures. Heavy use of zinc-containing denture adhesives is a classic cause of acquired copper deficiency.
Zinc upregulates metallothionein in enterocytes, which preferentially binds copper and traps it within the cells that are sloughed off, leading to severe systemic copper deficiency.

Key Concept

Excessive ingestion of zinc, classically from the overuse of zinc-containing denture adhesives in edentulous patients, causes profound copper deficiency. This manifests clinically as a myeloneuropathy mimicking B12 deficiency, alongside microcytic anemia and neutropenia.
Estimated Time:1m 30s
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Medical History Evaluation

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