Choice A. to aid with the diagnosis of SLE. If these are positive, further testing for more specific antibodies (eg, anti–double-stranded DNA, anti-Smith, anti–U1 ribonucleoprotein) should be undertaken.
Choice B. Many medications and illicit drugs (eg, amphetamines, corticosteroids, cocaine, hallucinogens, marijuana, bath salts) can cause psychosis via their CNS effects. However, amphetamines rarely cause psychosis when used in therapeutic dosages, and this patient has a normal creatinine level and no recent dosage changes. In addition, her drug screen is negative, indicating that she has not recently taken her amphetamines. Because amphetamine-induced psychotic disorder would not explain this patient's arthralgias, thrombocytopenia, proteinuria, and hematuria, checking antinuclear antibodies is the most appropriate next step.
Explanation
The acute onset of psychosis in a child or adolescent is rare, and it is essential to rule out medical or substance-induced conditions (see image) that are potentially reversible. This patient's history of arthralgia and psychosis, together with thrombocytopenia, hematuria, and proteinuria, is concerning for systemic lupus erythematosus (SLE). The classic malar rash seen in SLE is often absent and should not be relied on for diagnosis. Inflammatory disorders such as SLE can affect the CNS and manifest with both acute and chronic psychiatric symptoms, including psychosis, depression, mania, and anxiety.
Other neuropsychiatric manifestations seen in SLE include seizures, headaches, peripheral neuropathy, strokes, and chorea. Biological mechanisms of these manifestations are thought to include immune-mediated inflammation and vasculitis.
The most appropriate next step is to check for antinuclear antibodies to aid with the diagnosis of SLE. If these are positive, further testing for more specific antibodies (eg, anti–double-stranded DNA, anti-Smith, anti–U1 ribonucleoprotein) should be undertaken.
Educational objective: The sudden onset of psychosis in a child or adolescent is rare, and it is important to search for potentially reversible conditions such as medical disorders or substance use. Common medical conditions to rule out include systemic lupus erythematosus, thyroiditis, metabolic or electrolyte disorders, CNS infection, and epilepsy.
Choice D. Thyroiditis can result in anxiety, insomnia, and acute psychosis; however, the patient's TSH level is normal, making this diagnosis unlikely.
Choice E. An urethral swab could be used to detect gonococcal infection, which commonly presents as a migratory polyarthralgia in young people. Other manifestations include tenosynovitis, genitourinary symptoms, and skin lesions. However, gonococcal infection does not cause acute psychosis.
