A 14-year-old boy is brought to the pediatric clinic by his mother due to a 3-month histor… — USMLE Step 2 CK

A $14$ -year-old boy is brought to the pediatric clinic by his mother due to a $3$ -month history of declining academic performance, irritability, and social withdrawal. She reports that he frequently locks himself in his room and sometimes appears clumsy and disoriented when she enters abruptly. Physical examination reveals an erythematous, eczematous rash around his mouth and nose. Neurologic examination is significant for a broad-based, unsteady gait, dysarthria, and diminished deep tendon reflexes in the lower extremities. Laboratory studies show:

Laboratory Parameter	Result	Reference Range
Sodium	$138 \text{ mEq/L}$	$136$ - $145 \text{ mEq/L}$
Potassium	$2.8 \text{ mEq/L}$	$3.5$ - $5.0 \text{ mEq/L}$
Chloride	$115 \text{ mEq/L}$	$95$ - $105 \text{ mEq/L}$
Bicarbonate	$14 \text{ mEq/L}$	$22$ - $28 \text{ mEq/L}$
Blood urea nitrogen	$12 \text{ mg/dL}$	$7$ - $18 \text{ mg/dL}$
Creatinine	$0.7 \text{ mg/dL}$	$0.6$ - $1.2 \text{ mg/dL}$

Which of the following is the most likely diagnosis?

Inhalant use disorderCevap
B
Ethylene glycol toxicity
C
Phencyclidine intoxication
D
Synthetic cannabinoid intoxication
E
Dextromethorphan abuse

Cevap

The most likely diagnosis is inhalant use disorder, specifically secondary to toluene abuse.

The correct answer is inhalant use disorder, specifically toluene abuse. Toluene is a volatile solvent found in household products such as glues, paint thinners, and aerosols, and is frequently abused by adolescents due to its easy accessibility. Chronic inhalation causes a characteristic constellation of clinical findings. Dermatologically, the drying effects of hydrocarbons often lead to a perioral eczematous dermatitis colloquially known as "glue sniffer's rash." Neurologically, it causes prominent cerebellar signs (e.g., ataxia, dysarthria) and a peripheral neuropathy (manifesting as diminished deep tendon reflexes). Furthermore, toluene toxicity is classically associated with a Type 1 (distal) renal tubular acidosis. This presents laboratory findings of a hypokalemic, hyperchloremic, normal anion gap metabolic acidosis. This patient's calculated anion gap is 9 mEq/L, confirming a normal anion gap acidosis, which perfectly aligns with toluene-induced renal tubular acidosis.

Adım Adım Çözüm

Analyze the patient's physical examination findings.

The patient exhibits a perioral eczematous rash, broad-based ataxia, dysarthria, and hyporeflexia.

Identifying specific neurologic and dermatologic signs helps narrow the differential diagnosis among various substances of abuse.

Calculate the anion gap and interpret the laboratory results.

The anion gap is calculated as Sodium - (Chloride + Bicarbonate) = 138 - (115 + 14) = 9 mEq/L. This falls within the normal range (8-12 mEq/L). The patient therefore has a normal anion gap (hyperchloremic) metabolic acidosis combined with significant hypokalemia (2.8 mEq/L).

Acid-base status is crucial for distinguishing between different toxicological etiologies, particularly differentiating normal anion gap from high anion gap states.

Synthesize the clinical and laboratory data to identify the offending substance.

The combination of a "glue sniffer's rash", cerebellar signs, peripheral neuropathy, and Type 1 (distal) renal tubular acidosis is a pathognomonic presentation for chronic toluene toxicity.

Toluene, found in easily accessible products like glue and paint thinner, directly causes these unique dermatologic, neurologic, and renal manifestations.

Anahtar Kavram

Clinical presentation and laboratory findings of inhalant (toluene) use disorder

Soru

Cevap

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