Our results suggest that lithium treatment is not associated with significant clinical or neurometabolic alterations in SMD youth suffering from severe, functionally impairing, nonepisodic irritability and ADHD symptoms. Although our study is strengthened by the double-blind, placebo-controlled design combined with MRS, important limitations include significantly lower percentage of female SMD subjects randomized to lithium versus placebo, small sample size, the number of enrolled subjects who were not randomized, and short duration of treatment. Nevertheless, ours is the first RCT in SMD youth, highlighting the critical need for treatment studies (both pharmacologic and psychotherapeutic) in this common syndrome (Brotman et al.
2006; Leibenluft et al.
2006).
An important and unexpected finding is that 45% of the SMD youth made significant clinical improvement between admission to our inpatient child psychiatric research unit (baseline 1) and the end of the single-blind placebo run in (baseline 2). These children were not randomized because their clinical status improved throughout the medication withdrawal and placebo run-in phases to the point where they no longer met criteria for SMD. Prior studies of youth with irritability and CD with a similar design—i.e., randomization of only those who continued to meet criteria after inpatient admission and single blind placebo-run in—had randomization rates of 62% of initially admitted subjects (Campbell et al.
1995; Cueva et al.1996; Malone et al.
2000). Thus, our study's finding that a significant number of irritable youth improve with inpatient hospitalization aligns with previous trials of similar design. Because, by definition, the SMD youths had a chronic course of functionally impairing irritability, it is possible that those SMD youths who exhibited significant symptom improvement after admission were experiencing a protracted “honeymoon” phase that would have not persisted with time. However, our data may also demonstrate the powerful therapeutic impact of admission to a psychiatric research unit with highly skilled staff and teachers, working as a team to provide round-the-clock care and a structured milieu. Perhaps another reason for the SMD improvement following admission is a child's removal from environmental triggers, including parents or family members, teachers, or peers. Obviously, it would be important to identify the therapeutic factors that resulted in such clinical improvement prerandomization to guide future treatment of SMD symptoms, including irritability, in children and adolescents.
Importantly, specific psychotherapeutic interventions were not employed in our current study. Among the interventions potentially worth studying in SMD is creative problem solving (CPS), which has shown benefit in treating ODD, including significantly reduced numbers of restraints, seclusions, and patient/staff injuries on an inpatient unit after CPS was implemented versus before (Greene et al.
2003; Greene et al.
2004). Further study is also warranted to determine the impact of standardized daily routines and family therapy in treating the functionally disabling irritability of SMD youth, given prior studies showing such interventions benefit children and adults with mood disorders (Keitner et al.
1995; Frank et al.
1997; Miklowitz et al.
2000; Fristad et al.
2003; Pavuluri et al.
2004; Miklowitz et al.
2003; Rea et al.
2003).
The MRS data did not indicate significant differences between SMD youth treated with lithium and those treated with placebo. In BD adults, lithium treatment results in significantly decreased frontal mI and increased NAA (Moore et al.1999; Moore et al.
2000a; Silverstone et al.
2002; Silverstone et al.
2003). However, data in pediatric BD samples treated with lithium have been mixed. Davanzo et al. found that lithium treatment in BD youth was associated with decreased mI/Cr, but did not impact significantly on NAA/Cr or GLX/Cr in the anterior cingulate cortex (ACC) (Davanzo et al.
2001). Patel et al. (
2006) failed to show differences in mI, GLX, or Cr in the prefrontal cortex after lithium treatment (Patel et al.
2006), whereas Patel et al. (
2008) found that lithium treatment in depressed BD adolescents was associated with decreased medial prefrontal cortex, but not left or right lateral prefrontal cortex, NAA (Patel et al.
2008). One interpretation of our negative MRS findings is that the neurochemistry of SMD differs from that of BD. Indeed, whereas data indicate that BD youths have increased ACC mI/Cr and mI over those with intermittent explosive disorder or healthy controls (Davanzo et al.
2003), we recently found that, compared to healthy controls (
n
=

43), medication-free SMD youth (
n
=

36) had decreased, rather than increased, temporal mI/Cr (Dickstein et al.
2008). Moreover, while four of five studies of pediatric BD subjects, both medicated and medication-free, have demonstrated decreased frontal cortex NAA versus controls (Castillo et al.
2000; Cecil et al.
2003; Chang et al.
2003; Sassi et al.
2005; Olvera et al.
2007), our study of medication-free SMD youth showed no significant differences versus controls in frontal NAA/Cr, mI/Cr, Glx/Cr, or Cr.
Because of the small sample size, these data should be considered preliminary. Nonetheless, they do not support the use of lithium in SMD youth. Not only did the current study fail to detect lithium-placebo treatment differences, but the overall rate of improvement in the lithium group was relatively small, given prior findings on pharmacological responses in a range of pediatric mental syndromes. Thus, unfortunately, when considering other agents besides lithium, the prior literature that would guide treatment in these patients is very limited. Clinical trials to address the irritability and hyperarousal captured by the SMD criteria are hampered by the fact that the syndrome does not map well onto any DSM diagnosis.
Atypical antipsychotic medications may merit future study in SMD youth. In particular, risperidone is the first medication to receive a Food and Drug Administration (FDA) indication for the treatment of the core symptom of SMD, namely irritability. Specifically, risperidone now has a FDA indication for the treatment of irritability in PDD-spectrum illness based on two recent RCTs (McCracken et al.
2002; Shea et al.
2004), as well as an FDA indication for the treatment of pediatric BD. Other atypical antipsychotic medications have also shown promise in pediatric BD. Indeed, in a study by DelBello et al. demonstrating that BD adolescents whose acute mania remitted with olanzapine, this treatment was associated with significantly increased ventral prefrontal cortex NAA (Barzman et al.
2006; DelBello et al.
2002; DelBello et al.
2006). However, consideration of atypical antipsychotics for clinical or research purposes will need to incorporate measures of known side effects, such as metabolic syndrome (Correll et al.
2006).
Other antimanic agents, including antiepileptic drugs (AEDs), may also merit study in SMD youth. Divalproex has been shown to result in clinical improvement in youth with explosive temper and ODD or conduct disorder (Donovan et al.
1997; Donovan et al.
2000) as well as to reduce aggression in youth at high risk for BD (Saxena et al.
2006). Thus, divalproex may warrant further study in SMD youth. Carbamazepine is another AED that has been studied in treating irritability in children, adolescents, and adults (Mattes et al.
1984; Foster et al.
1989; Kowatch et al.
2000). However, in studies of children and adolescents, carbamazepine has not shown significant superiority to placebo in treating aggressive youth (Cueva et al.
1996), and a recent, large double-blind randomized placebo controlled trial of BD youth failed to demonstrate significant benefit from oxcarbazepine (Wagner et al.
2006).
Beyond antimanic agents, selective serotonin reuptake inhibitors (SSRIs) merit further study in SMD youths, given their role in treating disorders characterized by irritability, including MDD, anxiety disorders, premenstrual dysphoric disorder, and PDD (Fatemi et al.
1998; Birmaher et al.
2003; March et al.
2004; Owley et al.
2005; Ryan
2005). While concern regarding SSRI-induced increases in suicidal thinking precipitated the introduction of an FDA black-box warning, a recent meta-analysis of all pediatric trials of fluoxetine, sponsored by its manufacturer, showed no differences in aggression or hostility between those treated with drug versus placebo (Gibbons et al.
2006; Tauscher-Wisniewski et al.
2007).
Psychostimulants are a third important medication category that bear consideration in the treatment of SMD youth. Given that the “hyperarousal” symptoms of SMD consist of those symptoms common to ADHD and the “B” criteria of mania, there is necessarily a high rate of ADHD in youth with SMD. In addition, several studies suggest that stimulants may reduce aggression and hostility in patients with ADHD (Carlson et al.
2000; Connor et al.
2002; Sinzig et al.
2007). In sum, while a number of current medications may result in clinical improvement in children and adolescents suffering from psychiatric disorders involving irritability, our study of lithium is the first to study medication use specifically in SMD youths, and no significant difference in clinical outcome was noted.
As noted above, our study has several important limitations. Although it is possible that our sample size may contribute to a type II error, the very small effect size suggests that a very large study would be needed to detect a medication effect. Moreover, the overall low response rate to lithium suggests that this is not a promising treatment approach. While significantly fewer SMD girls than boys were randomized to lithium versus to placebo, few gender differences in lithium response have been identified in BD adults (Viguera et al.
2000; Viguera et al.
2001). It is also possible that SMD youth might have needed higher doses of lithium, longer duration of exposure, or both. Studies indicate that children have shorter elimination half-lives and greater lithium clearance than adults (Vitiello et al.
1988). Moreover, one study using lithium-7 MRS (rather than
1H-proton MRS) demonstrated that children (
n
=

9) had lower brain-to-serum lithium ratios than adults (
n
=

18) (Moore et al.
2002), suggesting that children may require higher serum levels of lithium to achieve the same brain concentrations. With respect to limitations of our MRS methodology, our study was modeled on prior work in BD adults, and thus evaluated neurometabolites in four ROIs, referenced to Cr to control for partial volume effects (Moore et al.
1999; Moore et al.
2000c). However, different MRS methodologies might yield different results; such methodologies might include using different ROI locations (e.g., anterior cingulate cortex), a whole-brain approach, or evaluating absolute concentrations with a higher strength magnetic field (Moore et al. 2000x; Davanzo et al.
2001). Resolution of these possibilities will require additional studies of lithium in SMD youth, maximizing their safe exposure to lithium while collecting clinical and neurometabolic data.