Somatic Symptom Disorders

Cognitive Behaviour therapy, 2016 voL. 45, no. 4, 259–269 http://dx.doi.org/10.1080/16506073.2016.1161663

© 2016 Swedish association for Behaviour therapy

The health preoccupation diagnostic interview: inter-rater reliability of a structured interview for diagnostic assessment of DSM-5 somatic symptom disorder and illness anxiety disorder

Erland Axelssona, Erik Anderssona, Brjánn Ljótssona, Daniel Wallhed Finnb and Erik Hedmana,c

aDivision of psychology, Department of Clinical neuroscience, Karolinska institutet, Stockholm, Sweden; bCapio psykiatri nacka, Stockholm, Sweden; cosher Center for integrative Medicine, Department of Clinical neuroscience, Karolinska institutet, Stockholm, Sweden

Introduction

The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association, 2013) has introduced several revisions of its predecessor (DSM-IV; American Psychiatric Association, 2000). One is that the DSM-IV somatoform disorders, including hypochondriasis and somatization disorder, have been abandoned. There were multiple reasons for this. The somatoform disorders were considered difficult to understand, and—despite their narrow criteria—showed a tendency to overlap (Dimsdale et al., 2013). Additionally, a common view was that these disorders overemphasized the presence of medically unexplained symptoms, i.e. that a medical explanation for the patient’s symptoms had to be ruled out for a psychiatric diagnosis to be made (Dimsdale et al., 2013). This praxis drew an unnecessarily sharp line between “medical” and “psychiatric” patients.

ABSTRACT Somatic symptom disorder (SSD) and illness anxiety disorder (IAD) are two new diagnoses introduced in the DSM-5. There is a need for reliable instruments to facilitate the assessment of these disorders. We therefore developed a structured diagnostic interview, the Health Preoccupation Diagnostic Interview (HPDI), which we hypothesized would reliably differentiate between SSD, IAD, and no diagnosis. Persons with clinically significant health anxiety (n = 52) and healthy controls (n = 52) were interviewed using the HPDI. Diagnoses were then compared with those made by an independent assessor, who listened to audio recordings of the interviews. Ratings generally indicated moderate to almost perfect inter-rater agreement, as illustrated by an overall Cohen’s κ of .85. Disagreements primarily concerned (a) the severity of somatic symptoms, (b) the differential diagnosis of panic disorder, and (c) SSD specifiers. We conclude that the HPDI can be used to reliably diagnose DSM-5 SSD and IAD.

KEYWORDS health anxiety; illness anxiety disorder; reliability; somatic symptom disorder; somatization

ARTICLE HISTORY received 24 november 2015 accepted 1 March 2016

CONTACT erland axelsson [email protected] Supplemental data for this article can be accessed here http://dx.doi.org/10.1080/16506073.2016.1161663

260 E. AxELSSon ET AL.

As a result, some diagnosed with a somatoform disorder (e.g. hypochondriasis) took offense at their somatic symptoms “being all in their head” (American Psychiatric Association, 2013; Dimsdale et al., 2013). It was also hard for clinicians to determine how many medical tests were necessary for a somatoform diagnosis (Dimsdale et al., 2013). These difficulties were likely among the reasons why the somatoform disorders were seldom diagnosed in clinical practice (American Psychiatric Association, 2013; Dimsdale et al., 2013; Rief & Martin, 2014).

The DSM-IV somatoform disorders have now been replaced with the DSM-5 somatic symptom and related disorders. Of these, somatic symptom disorder (SSD) and illness anxiety disorder (IAD) are likely to be most commonly diagnosed (American Psychiatric Association, 2013). In SSD the patient has (A) at least one somatic symptom (e.g. a local- ized pain) that causes significant distress or functional impairment. Related to the patient’s somatic symptoms is an excessive psychological reaction, involving either (B1) dispro- portionate interpretations of the somatic symptoms, (B2) anxiety about health or somatic symptoms, (B3) excessive time and energy devoted to health or somatic symptoms, or a combination of these B criteria. Although it is not necessary that one and the same somatic symptom is continuously present, (C) the state of being symptomatic has to have been persistent (“typically [for] more than 6 months”; American Psychiatric Association, 2013).

There are three specifiers for SSD. The (I) with predominant pain specifier is given when the patient’s somatic symptoms primarily involve pain. The (II) persistent specifier is given in the case of severe symptoms, marked impairment, and a duration longer than 6 months. The (III) current severity specifier can be defined as either mild, moderate, or severe. Mild implies that only one B criterion (B1, B2, or B3) is fulfilled, moderate means that at least two B criteria are fulfilled, and severe means that at least two B criteria are fulfilled and that there are either numerous somatic complaints or one very severe somatic symptom.

The core criterion of illness anxiety disorder (IAD) is (A) “a preoccupation with having or acquiring a serious illness” (American Psychiatric Association, 2013). There are (B) no or only mild somatic symptoms, and if the patient is likely to develop a medical condition, his or her preoccupation with health has to be excessive. The patient has (C) a high level of health-related anxiety and is easily worried about his or her health. Due to this fear, (D) the patient displays excessive health-related behaviors, such as repeated symptom-checking or avoidance of doctor visits. The (E) health preoccupation has been present for at least six months and is (F) not better explained by another psychiatric syndrome. IAD may be specified as care-seeking type (indicating frequent use of medical care) or care-avoidant type (indicating rare use of medical care).

In contrast to the DSM-IV somatoform disorders, the criteria of SSD and IAD do not require that the patient’s somatic symptoms are medically unexplained. Even if the somatic symptoms that are central to the health preoccupation are explained by a somatic disease, the patient may be given a diagnosis of SSD or IAD under the condition that the patient’s response to his or her somatic symptoms is significant and excessive. A patient with recur- rent dizziness due to poorly managed diabetes might for example be given a diagnosis of SSD if the dizziness is coupled with a persistent and disproportional fear of multiple sclerosis.

Although both SSD and IAD involve a preoccupation with health, there are also three important differences between these disorders. Firstly, SSD presupposes at least one somatic symptom (medically explained or not), which leads to significant distress or disruption of daily life. In contrast, IAD is given when there are no, or only minimal, somatic symptoms

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related to the health preoccupation. Secondly, whereas IAD requires health anxiety (defined here as a fear of having or acquiring a severe illness), SSD—strictly speaking—does not. Thirdly, IAD—like DSM-IV hypochondriasis—requires that the patient’s complaints have been present for at least six months, whereas the SSD duration criterion is more loosely formulated.

According to the DSM-5, roughly 75% of those meeting diagnostic criteria for DSM-IV hypochondriasis will now be classified as having SSD, whereas about 25% will have IAD (American Psychiatric Association, 2013). SSD is also meant to replace both DSM-IV som- atization disorder, undifferentiated somatoform disorder and pain disorder (Dimsdale et al., 2013). Under our interpretation, a typical health anxiety patient either has SSD or IAD, but not a combination of the two. In the case of an enduring and excessive fear of severe illness, the key question is typically whether the patient’s somatic symptoms are mild enough to warrant a diagnosis of IAD (rather than SSD). If significant health anxiety is coupled with recurring somatic symptoms that are reasonably distinct, the patient should typically be given a diagnosis of SSD (but not IAD). In rare cases, patients with significant health anxiety might not qualify for either of the two diagnoses. This could, for example, be the case if the patient has a persistent fear of severe illness, but neither somatic symptoms nor excessive health-related behaviors.

In the DSM-5 field trials, SSD (then referred to as “complex somatic symptom disorder revised”) demonstrated substantial inter-rater reliability (κ = .61), but was never assessed together with IAD (Freedman et al., 2013). Over and above these field trials, to our knowl- edge, only four studies have attempted to study DSM-5 SSD and/or IAD, but in doing so have relied exclusively on post hoc classification based on self-assessment questionnaires (Bailer et al., 2016; Häuser, Bialas, Welsch, & Wolfe, 2015; van Dessel, van der Wouden, Dekker, & van der Horst, 2016; Voigt et al., 2012).

Since structured interviews are known to enhance the reliability of psychiatric diagnostic procedures (Basco et al., 2000; Grove, Andreasen, McDonald-Scott, Keller, & Shapiro, 1981; Kranzler et al., 1995), there is a need for reliable diagnostic instruments to aid clinicians in assessing new diagnoses introduced in the DSM-5. We therefore aimed to develop and investigate the psychometric properties of a structured interview for DSM-5 SSD and IAD. We hypothesized that this new interview would prove reliable in differentiating between SSD, IAD, and no diagnosis (ND).

Methods

Participants

The present study included both participants with severe health anxiety and healthy controls as respondents for diagnostic interviews. All respondents were recruited via newspaper advertisements and subsequent self-referral via the Internet. The healthy control respond- ents (n = 52) were compensated with two lottery tickets for their participation. Respondents with severe health anxiety (n = 52) were not compensated in this manner, but instead applied for a clinical trial of cognitive behavior therapy. Information concerning this clinical trial was sent to health care providers in Stockholm and Gothenburg, Sweden. The clinical trial had 214 applicants that were interviewed. From these applicants we randomly selected a

262 E. AxELSSon ET AL.

sample stratified for age so that it would match the age distribution of the healthy control group. Participant data is presented in Table 1.

Materials

The Health Anxiety Inventory (HAI) is a well-established self-report measure of health anx- iety; primarily of cognitive and emotional factors associated with DSM-IV hypochondriasis (Salkovskis, Rimes, Warwick, & Clark, 2002). The HAI comprises 64 items, each with a scale of 4 alternatives (e.g. between “I do not worry about my health.” and “I spend most of my time worrying about my health.”), rendering a total HAI score between 0 and 192. The HAI has good psychometric properties when administered via the Internet (Hedman et al., 2015).

The Mini-International Neuropsychiatric Interview 6 (MINI; Sheehan et al., 1998) is a structured diagnostic interview for the assessment of common psychiatric disorders, including anxiety disorders and major depressive disorder. In the present study, diagnostic assessments were based on all MINI modules except that for antisocial personality disorder.

We developed the Health Preoccupation Diagnostic Interview (HPDI) with the aim of discriminating between DSM-5 SSD and IAD, and also to discriminate persons with SSD or IAD from persons without these disorders (the interview is presented in Appendix 1). Items for the HPDI were formulated, discussed, and revised by clinical psychologists with extensive experience in assessing and treating DSM-IV hypochondriasis. A first draft of the instrument was pilot tested in a small sample of patients seeking help for psychiatric disorders in the mental health department of a community health center.

After this test phase, items were further revised to increase accuracy and usability. The interview finally encompassed 42 items, of which 24 were questions to the respond- ent and 18 to the interviewer. For each diagnostic criterion, the general principle was that the HPDI would first provide the interviewer with one or more questions to extract pertinent information from the respondent (e.g. “Have you recently been worried about having or developing a serious illness?”, “Which illnesses have you been afraid of having or developing?”), and then prompt the interviewer to decide if the corresponding cri- terion was met (e.g. “Does the patient show a preoccupation with having or acquiring a serious illness?”).

Table 1. Description of respondents.

Note. the p-values are based on Student’s t-test and χ²-test. Cta, clinical trial applicants; hai, health anxiety inventory; hC, healthy controls; iaD, illness anxiety disorder; nD, no diagnosis; SSD, somatic symptom disorder.

aDiagnosis according to the interviewer.

Combined sample (N = 104)

Clinical trial applicants (n = 52)

Healthy controls (n = 52)

CTA vs HC

age, range 18–73 20–69 18–73 age, mean (SD) 40.5 (13.1) 38.5 (12.9) 42.4 (13.1) p = .14 Female, n (%) 76 (73%) 40 (77%) 36 (69%) p = .38

hai, range 10–150 75–150 10–62 hai, mean (SD) 70.2 (41.6) 107.8 (21.6) 32.7 (12.1) p < .01

SSD, n (%)a 42 (40%) 42 (81%) 0 (0%) p < .01iaD, n (%)a 7 (7%) 7 (14%) 0 (0%)

nD, n (%)a 55 (53%) 3 (6%) 52 (100%)

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Procedure

All respondents, both clinical trial applicants and healthy controls, completed the HAI via the Internet. They were then asked routine clinical questions (such as “Do you have—or have you ever had—a somatic disease out of the ordinary?”) and assessed for psychiat- ric syndromes using the MINI followed by the HPDI. This was done through telephone interviews, which is a reliable method of diagnostic assessment (Rohde, Lewinsohn, & Seeley, 1997). All interviews were recorded using a digital voice recorder with an external telephone pick-up microphone. We then applied the procedure of Skre, Onstad, Torgersen, and Kringlen (1991), by which an independent assessor blind to the diagnoses made by the interviewer listened to the recorded interviews and, using the HPDI, determined if patients met diagnostic criteria for SSD or IAD.

In order to ensure that the assessor was blind to previous diagnoses, the interviewer was instructed not to inform the respondent of any diagnostic considerations. As long as the respondent expressed even a vague tendency to identify with the diagnostic criteria probed, the interviewer strived to always complete the full HPDI, in order not to reveal any diagnostic decisions. This included assessing most IAD items regardless of whether an SSD diagnosis had previously been made or not. To prevent diagnostic ratings from being steered by sample-related expectations (e.g. that healthy controls would not qualify for a diagnosis), the assessor was also blind to whether respondents belonged to the clinical trial applicant sample or the healthy control sample. In order to ensure this, all audio files were assigned randomized identification numbers and date stamps were removed.

Both the interviewer and the assessor had access to the DSM-5 and were instructed to consult it when needed. If the assessor required information about the presence of comorbid psychiatric syndromes (e.g. whether or not a certain respondent suffered from panic dis- order) in order to make a decision concerning the presence of SSD or IAD, relevant results of the MINI interview were provided (this occurred in 7 of all 104 cases).

There was also a second assessor who listened to the recorded interviews. This assessor proposed a combined diagnosis of SSD and IAD in 41 (39%) of all 104 cases. Combining SSD and IAD should only be possible in cases where (a) SSD does not involve significant health anxiety (a fear of severe illness), but rather some other form of health preoccupation (e.g. kinesiophobia due to pain), and (b) there is a significant health anxiety which is either unrelated to somatic symptoms or only coupled with mild somatic symptoms (so that an IAD diagnosis can be made). Since the present study involved healthy controls and a sig- nificantly health anxious sample, SSD unrelated to health anxiety was expected to be rare, and the combination of SSD and IAD therefore highly unlikely. Since the second assessor clearly misunderstood the DSM-5 diagnostic criteria, data from this assessor was excluded from further analysis but is available from the authors on request.

After completing the reliability study, we made minor alterations to the HPDI in order to make it more user-friendly. SSD item 2, SSD item 8, and IAD item 4 were somewhat simplified, as their latter parts were made optional and put in parentheses. We also made clear that the follow-up question of SSD item 5 should be posed if the patient’s somatic symptoms are not know to be explained by a serious disease. As SSD item 13 was rarely understood by the respondents, the phrase “During the present episode, how long have you felt distressed or hindered” was changed to “How long have you been concerned.” IAD item 9 was altered in a similar way. In order to enhance the reliability of the SSD pain specifier,

264 E. AxELSSon ET AL.

a new question was added (SSD item 14). Finally, in order to prevent misunderstandings similar to that of the second assessor, we added a reminder to consider IAD in the case of mild somatic symptoms. We think it highly unlikely that these minor simplifications will in any way have a negative impact on the reliability of the instrument.

Clinicians

All telephone interviews were conducted by the same interviewer, a resident clinical psy- chologist with experience of conducting about 120 diagnostic telephone interviews with persons seeking treatment for health anxiety. The interviewer received supervision by a doctoral-level licensed psychologist specialized in diagnosis and treatment of health anxiety. The assessor whose ratings were included in the main analysis was a psychology student in the final year of the master level psychology program. During the project, the assessor periodically discussed diagnostic principles (e.g. guidelines for differential diagnosis) with other members of the research team. However, in order to ensure assessment integrity, specific cases were never mentioned.

Statistical analysis

Cohen’s κ was calculated for the inter-rater agreement on SSD vs. IAD vs. ND cases, using the SPSS version 22.0 (IBM Corp., Armonk, NY). As omnibus reliability estimates (such as the κ) are sometimes hard to interpret (Cicchetti & Feinstein, 1990), we also calculated (a) the absolute number of cases agreed, (b) the percentage of cases agreed, (c) the number of cases agreed per class (e.g. the number of SSD diagnoses that overlapped), and (d) the proportion of agreed cases per class (e.g. the percentage of SSD diagnoses that overlapped). The latter was done by dividing the number of agreed cases within each class (e.g. the number of SSD diagnoses agreed on) by the mean number of cases assigned to the class (e.g. the total number of SSD diagnoses made by both raters, divided by two). Such a ratio may be thought of as a “positive predictive value” indicating how likely a diagnosis (e.g. of SSD) determined by one rater was to be endorsed by the other rater. Kappa values and the corresponding indexes of agreement were also calculated for the inter-rater agreement on SSD and IAD diagnostic specifiers. Verbal interpretations of Cohen’s κ followed the cate- gorical divisions of Landis and Koch (1977). Hence, “poor” means κ < 0.00, “slight” means 0.00 ≤ κ ≤ 0.20, “fair” means 0.21 ≤ κ ≤ 0.40, “moderate” means 0.41 ≤ κ ≤ 0.60, “substantial” means 0.61 ≤ κ ≤ 0.80, and “almost perfect” means 0.81 ≤ κ ≤ 1.00.

Results

Choosing between SSD, IAD, and ND, the interviewer and the assessor agreed in 95 (91%) of all 104 cases. No respondent was diagnosed with both SSD and IAD by the same clini- cian. Kappa values and proportion of agreed cases are presented in Table 2. As shown in Table 3, agreement on diagnosis specifiers was almost perfect concerning IAD specifiers, moderate concerning the SSD pain specifier, and slight to fair concerning the SSD persis- tence and severity specifiers. Post hoc weighted κ estimates for the severity specifier were roughly similar.

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With regard to diagnosis, the interviewer and the assessor disagreed over nine cases. Five of these were rated as SSD by the interviewer and IAD by the assessor. This was primarily due to disagreement about which somatic symptoms should be considered mild enough to permit an IAD—rather than an SSD—diagnosis. Three cases were rated as SSD by the

Table 2. reliability estimates of inter-rater agreement on SSD, iaD, and nD.

Note. iaD, illness anxiety disorder; nD, no diagnosis; SSD, somatic symptom disorder. anot applicable due to division by zero. bnumber of cases agreed divided by the average total number of cases per rater. in other words, the likelihood of a diagnosis

by one rater to be endorsed by the other rater (see “Statistical analysis”).

Combined sample Clinical trial applicants Healthy controls agreement, total (SSD vs. iaD vs. nD) Cohen’s κ .85 .59 n/a a

agreed, n (%) 95 (91.3%) 43 (82.7%) 52 (100%) Disagreed, n (%) 9 (8.7%) 9 (17.3%) 0 (0%)

agreement, positive cases agreed SSD, n (%b) 34 (88%) 34 (88%) 0 (n/a a) agreed iaD, n (%b) 6 (67%) 6 (67%) 0 (n/a a) agreed nD, n (%b) 55 (97%) 3 (67%) 52 (100%)

agreement, SSD vs. non-SSD Cohen’s κ .82 .56 n/a a

agreed, n (%) 95 (91.3%) 43 (82.7%) 52 (100%) Disagreed, n (%) 9 (8.7%) 9 (17.3%) 0 (0%)

agreement, iaD vs. non-iaD Cohen’s κ .64 .60 n/a a

agreed, n (%) 97 (93.3%) 45 (86.5%) 52 (100%) Disagreed, n (%) 7 (6.7%) 7 (13.5%) 0 (0%)

agreement, nD vs. non-nD Cohen’s κ .94 .64 n/a a

agreed, n (%) 101 (97.1%) 49 (94.2%) 52 (100%) Disagreed, n (%) 3 (2.9%) 3 (5.8%) 0 (0%)

Table 3. reliability estimates of inter-rater agreement on SSD and iaD specifiers.

Note. estimates are based on cases where the interviewer and the assessor agreed on an SSD or iaD diagnosis. iaD, illness anxiety disorder; SSD, somatic symptom disorder.

anot applicable due to division by zero. bnumber of cases agreed divided by the average total number of cases per rater. in other words, the likelihood of a specifier

by one rater to be endorsed by the other rater (see “Statistical analysis”).

Specifier Cohen’s κ Agreed per choice, n (%) Agreed per class, n (%b)

SSD (n = 34) Mild .08 11 (32%) 1 (18%) vs Moderate 4 (29%) vs Severe 6 (39%)

predominantly pain .45 30 (88%) 2 (50%) vs not predominantly pain 28 (93%)

persistent .30 24 (71%) 5 (50%) vs not persistent 19 (79%)

iaD (n = 6) Care-seeking 1 6 (100%) 4 (100%) vs Care avoidant 2 (100%) vs no specifier 0 (n/aa)

266 E. AxELSSon ET AL.

interviewer and ND by the assessor. Two of these were cases of panic disorder, where disagreement arose as to whether an additional diagnosis of SSD should be made or not, and one case mainly had to do with the clinicians disagreeing on whether the patient’s health anxiety returned with sufficient frequency to warrant a diagnosis. The remaining disagreement—where the interviewer suggested IAD and the assessor SSD—stemmed from different views on whether the somatic symptoms of the respondent were frequent enough to warrant an SSD—rather than an IAD—diagnosis.

In the clinical trial applicant sample, 11 out of 52 respondents (21%) reported presently having at least one organic disease “out of the ordinary.” The only conditions that were referred to by more than one respondent were hypothyroidism (n = 3) and fibromyalgia syndrome (n = 2). Other medical conditions included a benign brain tumor, hiatus hernia, irritable bowel syndrome, immunodeficiency, an unspecified benign brain malformation, spinal disc herniation, severe asthma, severe migraine, and vulvar vestibulitis. Among the healthy controls, only one respondent reported having a medical condition worthy of men- tioning (hypothyroidism).

Discussion

This study investigated the psychometric properties of the Health Preoccupation Diagnostic Interview (HPDI): a new structured interview for diagnosing DSM-5 SSD and IAD. The results suggest that the HPDI can be a reliable diagnostic instrument for assessing health anxiety in terms of SSD and IAD. An important strength of this study was that the clinicians who assigned diagnoses did not undergo any special training to increase rating concordance. This means that the presented estimates are likely to mirror what would be attainable in clinical practice. To our knowledge, this study is the first to show that these new DSM-5 diagnoses can be simultaneously assessed with acceptable inter-rater reliability.

The overall (SSD vs. IAD vs. ND) agreement was almost perfect for the combined sample, moderate for the clinical sample, and perfect (κ not applicable) for the healthy controls. Notably, as the assessor was blind to respondent recruitment procedures, sample differ- ences in diagnostic ratings cannot be explained by mere expectancy: e.g. that the assessor expected non-clinical respondents not to meet diagnostic criteria. The results are in line with previous reliability estimates for many diagnoses made with the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID I; Lobbestael, Leurgans, & Arntz, 2011; Skre et al., 1991) but slightly lower than the reliability estimates of most MINI modules (Sheehan et al., 1998). Additional standardization of the assessment procedure could possibly further enhance the psychometric properties of the HPDI. In the present study, disagreement as to whether a diagnosis of SSD or IAD should be made primarily arose due to different views on how severe certain somatic symptoms were. Therefore, if more precise definitions of “mild” or “minimal” somatic symptoms were established, many disagreements could probably be avoided. For research purposes, the use of multiple co-operating raters and/or introductory rating concordance checks could also be used to further enhance reliability figures.

Although there was almost perfect agreement on the IAD specifiers, i.e. care seeking or care avoidant subtypes, and moderate agreement on the SSD pain specifier, there was much higher disagreement on the SSD severity and persistence specifiers. We see two likely reasons for this. Firstly, as pointed out by Rief and Martin (2014), the names of these specifiers are surprising. Most strikingly, as SSD criterion C ensures that most SSD patients have had

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their symptoms for six months or longer, the persistence specifier is primarily a measure of symptom severity and functional impairment. That is, the persistence specifier is—at least in most cases—not a measure of persistency at all. Similarly, the SSD severity specifier seemed only vaguely related to the respondent’s degree of suffering and impairment.

Secondly, expanding on our previous suggestions for further operationalization of “mild” somatic symptoms, what exactly is a “severe” or “very severe” somatic symptom? And how many are “multiple” somatic complaints? We deliberately refrained from making such clar- ifications, in order not to arbitrarily divert from the DSM-5 criteria. Unfortunately, these criteria do not seem to in and of themselves provide sufficient guidance for the assessment of the above-mentioned specifiers. Simply put, we suspect that the SSD severity and persis- tence specifiers, as phrased in DSM-5, are too vague and counterintuitive to be sufficiently reliable. In future revisions of the DSM, we strongly suggest that these specifiers be better operationalized.

The primary limitation of this study was that only two clinicians’ assessments could be compared. Even though the assessor was blind to the respondent recruitment procedure, the interviewer was not, and might therefore—although instructed not to do so—have steered the interview based on expectancy (so that individuals of the non-clinical sample were treated differently than individuals of the clinical trial applicant sample). There is also a possibility that reliability figures had been different (either better or worse) if the assessor had conducted separate diagnostic interviews instead of listening to audio files.

Even though the structured diagnostic interview covered many common differential diagnoses of SSD and IAD (such as major depressive disorder, panic disorder, generalized anxiety disorder, and obsessive-compulsive disorder), several conditions of the DSM were not surveyed in such a systematic manner. Of particular interest, the remaining somatic symptom and related disorders (e.g. conversion disorder and the psychological factors affecting other medical conditions category), as well as sexual dysfunction disorders (e.g. genito-pelvic pain/penetration disorder) were not routinely assessed using separate prompts or modules.

There were also limitations with regard to sampling. Since the two samples of this study (health anxious versus non-clinical respondents) were recruited through different channels, it is likely that the clinicians’ (the interviewer’s and the assessor’s) ability to distinguish between diagnostic (SSD or IAD) cases and ND cases was slightly overestimated. Since IAD was more rare than SSD and ND, reliability estimates for IAD are also likely less gen- eralizable than those for SSD and ND. The presented findings nevertheless indicate that the HPDI shows great promise in diagnosing both SSD and IAD.

Although the HPDI likely makes the diagnostic procedure easier, it is worth underscoring that structured diagnostic interviews (like the HPDI) demand that their user is familiar with the diagnoses being assessed (in this case DSM-5 SSD and IAD). This may seem obvious, but was made even more evident by the misunderstanding on behalf of one of two assessors in the present study (see “Procedure”). The criteria of SSD and IAD may seem counterintu- itive, not least since most clinicians are not used to classifying somatic symptoms in terms of severity. Nevertheless, as we have seen, determining somatic symptom severity is often important to differentiate SSD from IAD. A thorough understanding of common differential diagnoses, such as anxiety and obsessive-compulsive spectrum disorders, is also required in order to make a valid diagnosis.

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We conclude that the HPDI can be a reliable instrument for diagnosing DSM-5 SSD and IAD. It should, however, only be used by clinicians familiar with the DSM-5, and is not suit- able for assessing the SSD severity and persistence specifiers. The psychometric properties of the HPDI should preferably be further investigated in additional patient groups (e.g. mixed psychiatric samples, patients with chronic pain, patients suffering from severe illness, and samples involving more patients with IAD). Since the completion of this study, modules for SSD and IAD have been included in the Structured Clinical Interview for DSM-5 (SCID- 5; American Psychiatric Association, 2015) and Anxiety and Related Disorders Interview Schedule for DSM-5 (ADIS-5; Brown & Barlow, 2014), but the psychometric properties of these modules have—to our knowledge—not yet been evaluated. A promising SSD B criteria symptom questionnaire has also been developed by Toussaint et al. (2016). We warmly welcome all efforts that help shed further light on SSD, IAD, and the relationship between these disorders. Free use of the HPDI is encouraged in order to achieve this end.

Authors’ contributions

Conception and design: primarily EAx and EH. Procedure and data acquisition: EAx, EAn, BL, and EH. All authors—EAx, EAn, BL, DWF, and EH—contributed significantly to the analysis, interpretation, and writing process. All authors read and approved the final manuscript.

Acknowledgment

We thank MSc Rebecka Bratt for her skillful and invaluable contributions to this project.

Disclosure statement

The authors declare that they have no conflicts of interest.

Funding

This research was funded by Karolinska Institutet and Stockholm County Council, which had no role in the design, realization, or publication of the study.

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