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Zorluk: ZorSubstance-Related and Addictive Disorders

Parents bring their 1616-year-old son to the acute care clinic due to the sudden onset of profound lower extremity weakness. The patient states that his legs feel "like jelly" and he is unable to stand independently. Over the past several months, his parents have noted a significant decline in his academic performance, increased irritability, and a tendency to isolate himself in the family's poorly ventilated detached garage for hours. Vital signs are within normal limits. Physical examination reveals flaccid paralysis of the bilateral lower extremities with absent deep tendon reflexes. A well-demarcated, erythematous, scaling dermatitis is noted surrounding his mouth and nares. His breath emits a faint, sweet, chemical odor. Laboratory studies are obtained and reveal the following:

Laboratory testResultReference range
Sodium138 mEq/L138 \text{ mEq/L}136−145 mEq/L136-145 \text{ mEq/L}
Potassium1.8 mEq/L1.8 \text{ mEq/L}3.5−5.0 mEq/L3.5-5.0 \text{ mEq/L}
Chloride115 mEq/L115 \text{ mEq/L}95−105 mEq/L95-105 \text{ mEq/L}
Bicarbonate12 mEq/L12 \text{ mEq/L}22−28 mEq/L22-28 \text{ mEq/L}
Blood urea nitrogen14 mg/dL14 \text{ mg/dL}7−18 mg/dL7-18 \text{ mg/dL}
Creatinine0.9 mg/dL0.9 \text{ mg/dL}0.6−1.2 mg/dL0.6-1.2 \text{ mg/dL}

Which of the following is the most likely primary mechanism underlying this patient's clinical presentation and laboratory findings?

  1. Impaired hydrogen ion excretion in the distal renal tubuleCevap
  2. B
    Accumulation of unmeasured acidic metabolic byproducts
  3. C
    Defective reabsorption of filtered bicarbonate in the proximal renal tubule
  4. D
    Excessive gastrointestinal elimination of potassium and bicarbonate
  5. E
    Noncompetitive antagonism of N-methyl-D-aspartate receptors

Cevap

Impaired hydrogen ion excretion in the distal renal tubule
The correct answer is impaired hydrogen ion excretion in the distal renal tubule. This patient's presentation of perioral dermatitis ('glue sniffer's rash'), sweet chemical odor, behavioral changes, and garage isolation is highly characteristic of inhalant abuse, specifically toluene. Toluene toxicity famously causes a Type 11 (distal) renal tubular acidosis (RTA) by impairing hydrogen ion excretion in the distal renal tubule. This primary defect leads to a normal anion gap metabolic acidosis (NAGMA) and severe urinary potassium wasting. The resulting profound hypokalemia manifests clinically as flaccid paralysis, areflexia, and severe muscle weakness.

Adım Adım Çözüm

1
Calculate the serum anion gap to classify the metabolic acidosis.
Anion gap = Na - (Cl + HCO3) = 138 - (115 + 12) = 11 mEq/L.
Determining if the acidosis is a normal or high anion gap narrows the differential diagnosis for toxic ingestions and metabolic disturbances.
2
Identify the clinical syndrome based on the metabolic profile and physical exam findings.
The patient has a normal anion gap metabolic acidosis (NAGMA) with severe hypokalemia, flaccid paralysis, and a classic perioral "glue sniffer's rash".
Synthesizing the lab data (hypokalemia + NAGMA) with the unique dermatologic and behavioral clues points to a specific toxic etiology.
3
Determine the pathophysiologic mechanism of the suspected toxicity.
Toluene inhalation causes Type 1 renal tubular acidosis by impairing distal tubule hydrogen ion excretion.
Matching the toxin (toluene) to its physiological effect on the kidneys confirms the correct underlying mechanism.

Anahtar Kavram

Toluene inhalation (inhalant abuse) causes a Type 1 (distal) renal tubular acidosis, characterized by a normal anion gap metabolic acidosis and severe hypokalemia that can present with rapidly progressive flaccid paralysis.
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Substance-Related and Addictive Disorders

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