There is increasing evidence of differences in demographic and clinical characteristics of OCD patients with and without schizotypal features, supporting the clinical validity of a schizotypal subgroup of OCD (Eisen and Rasmussen 1993; Matsunaga et al. 2000; Sobin et al. 2000; Torres et al. 2006; Catapano et al. 2010; Brakoulias et al. 2014). Early age of onset, male gender, and a history of specific phobia have been shown to increase the risk of schizotypy in patients with OCD. In addition, schizotypal OCD patients are more likely to be single and unemployed. Similar to studies in nonclinical samples, most but not all clinical studies link positive symptoms of schizotypy with OCS (Einstein and Menzies 2004; Enright and Beech 1993; Lee and Telch 2005; Poyurovsky et al. 2008). Notably, marked intercorrelations have been found between positive schizotypal symptoms and indicators of OCD severity, including earlier age of onset, comorbid diagnoses, and treatment resistance (Moritz et al. 2004; Sobin et al. 2000). Compared to OCD patients, those with schizotypal OCD exhibit higher rates of symmetry/order obsessions, ordering/arranging, and checking and counting compulsions (Sobin et al. 2000; Brakoulias et al. 2014). Hoarding seems to be associated with somewhat higher levels of schizotypal features. Hoarders are significantly more likely to have more severe psychopathology, poorer insight, higher prevalence of comorbid schizotypal or obsessive-compulsive personality disorder, closer association with symmetry dimension, and poorer treatment outcome (Frost et al. 2000; Matsunaga et al. 2010).

Axis I comorbid psychiatric disorders are highly prevalent in patients with schizotypal OCD and are associated with additional morbidity. Similar to “pure” OCD patients, two-thirds of patients with schizotypal OCD have at least one additional comorbid disorder (Poyurovsky et al. 2008). Major depressive disorder appeared to be the most common (roughly 50 %), followed by anxiety disorders (panic disorder, social and simple phobias), and OCD-spectrum disorders (tic disorders, body dysmorphic disorder). Whether patients with schizotypal OCD are more susceptible for developing schizophrenia compared to their “pure” OCD counterparts are yet to be clarified and merit prospective investigations.

Schizotypal personality disorder predicts poor response to standard pharmacological and behavioral intervention in OCD patients. Jenike et al. (1986) retrospectively examined characteristics of 43 treatment-resistant obsessive-compulsive patients and found that those with concomitant schizotypal personality disorder had a higher rate of treatment failure. Of the 29 treated OCD patients without schizotypal personality disorder, 26 (90 %) improved at least moderately, and only one of 14 (7 %) schizotypal OCD patients improved. The same authors conducted a controlled 12-week trial of clomipramine among 55 patients with OCD and confirmed that the presence of schizotypal personality disorder was a strong predictor of poor treatment outcome (Baer et al. 1992). These results were substantiated by Ravizza et al. (1995) who found that poorer response to either clomipramine or fluoxetine was predicted in a stepwise multiple regressions by (1) concomitant schizotypal personality disorder, (2) presence of compulsions, and (3) longer duration of illness. Similarly, in a 3-year prospective naturalistic study of OCD patients, significant predictors of poor outcome included longer duration of illness, a greater severity of obsessive-compulsive symptoms at intake, and the presence of comorbid schizotypal personality disorder (Catapano et al. 2006).

Not all studies found an association between schizotypal personality disorder and nonresponse to treatment in patients with OCD. It was hypothesized that a binary approach (presence vs. absence of schizotypal personality) may obscure the relation between schizotypal personality disorder and treatment outcome (Moritz et al. 2004). The authors investigated whether the predictive importance of schizotypal personality is confined to a subset of symptoms of schizotypy. In 53 patients with OCD who underwent multimodal cognitive behavioral therapy, stepwise regression analysis revealed that, indeed, elevated scores in the positive but not negative schizotypal factor, especially perceptual aberrations, strongly predicted treatment failure.

Overall, the presence of schizotypal personality disorder, particularly its positive psychopathological dimension, seems to increase the risk of treatment failure in OCD patients with as many as 25 % of schizotypal OCD patients failing to experience any improvement with treatment (Ravizza et al. 1995; Erzegovesi et al. 2001).

Two pharmacological augmentation strategies for nonresponders to serotonin reuptake inhibitors (SRIs) have been studied. The first strategy involved the use of serotonin-enhancing agents (e.g., lithium, clonazepam, or buspirone) to maximize treatment response and yielded unanimously discouraging results. The second involved the addition of low-dose dopamine antagonists to SRIs. The rationale for adding dopamine antagonists is based on the assumption of the involvement of the dopaminergic system in addition to the serotonergic system in the mediation of obsessive-compulsive symptoms and putative treatment resistance. This seems to be particularly relevant in schizotypal personality disorder comorbid to OCD (Coccaro 1998; Koenigsberg et al. 2003). Indeed, starting with small open-label studies, the presence of schizotypal personality disorder seemed to herald positive response to antipsychotic augmentation in SRI-resistant OCD.

McDougle et al. (1990) explicitly examined whether comorbid schizotypal personality disorder and tic spectrum disorders were associated with a positive response to the addition of a neuroleptic (pimozide, mean dose = 6.5 mg/day; thioridazine, mean dose = 87.5 mg/day; or thiothixene, 6 mg/day) in OCD patients who did not respond to fluvoxamine. On the basis of the Clinical Global Impression scale criterion of improvement, 9 (53 %) of 17 participants responded, 7 (88 %) of 8 patients with comorbid tic or schizotypal personality disorder responded; however, only 2 (22 %) of 9 patients without these disorders responded (P = 0.02, Fisher’s exact test). The addition of antipsychotic agents however was not without cost. More than half of the patients experienced mild to moderate extrapyramidal side effects after the addition of the neuroleptic agent.

Promising results were also obtained when the efficacy of olanzapine addition to fluvoxamine-refractory OCD patients was investigated (Bogetto et al. 2000). Twenty-three OCD nonresponders to a 6-month, open-label trial with fluvoxamine (300 mg/day) entered a 3-month open-label trial of augmentation with olanzapine (5 mg/day). Ten patients (43.5 %) were rated as responders, and concomitant schizotypal personality disorder was the only factor significantly associated with response.

McDougle et al. (2000) conducted a double-blind placebo-controlled study of risperidone addition in OCD patients refractory to SRIs. Fifty percent of the risperidone-treated study completers (9 of 18) were responders (mean daily dose, 2.2 ± 0.7 mg/day) compared with none of 15 in the placebo addition group (P < 0.005). There was no difference, however, in response between OCD patients with and without comorbid diagnoses of schizotypal personality disorder.

Our comparative study of treatment-seeking OCD patients with and without schizotypal personality disorder revealed a significant difference between the two groups in the proportion of patients who required antipsychotic augmentation (Poyurovsky et al. 2008). Thus, 73 % (11 of 15 patients) in the schizotypal OCD group compared to 26 % (8 of 31 patients) were prescribed antipsychotic augmentation (haloperidol, 2.5 mg/day, risperidone, 0.5–1.5 mg/day, or olanzapine 5–10 mg/day). This study supported clinical experience that indicated that treatment-seeking schizotypal OCD patients most probably require an SRI and antipsychotic agent combination to address both components of their complex psychiatric condition. Notably, the role of psychotherapy in the management of schizotypal OCD patients has not been addressed in this study.

In a comprehensive systematic review, Bloch et al. (2006) strongly supported the clinical utility of low-dose antipsychotic augmentation as an effective intervention for treatment-refractory OCD patients. However, the evaluation of the role of comorbid schizotypal personality disorder was notably absent in this and other more recent reviews (Bandelow et al. 2008; Muscatello et al. 2011) most probably because of the insufficient number of studies with randomized controlled trial methodology required to be included in the review.