Pain and functional neurological disorder: a systematic review and meta-analysis.

BACKGROUND: Functional neurological disorder (FND) is characterised by neurological symptoms, such as seizures and abnormal movements. Despite its significance to patients, the clinical features of chronic pain in people with FND, and of FND in people with chronic pain, have not been comprehensively studied. METHODS: We systematically reviewed PubMed, Embase and PsycINFO for studies of chronic pain in adults with FND and FND in patients with chronic pain. We described the proportions of patients reporting pain, pain rating and timing, pain-related diagnoses and responsiveness to treatment. We performed random effects meta-analyses of the proportions of patients with FND who reported pain or were diagnosed with pain-related disorders. RESULTS: Seven hundred and fifteen articles were screened and 64 were included in the analysis. Eight case-control studies of 3476 patients described pain symptoms in a higher proportion of patients with FND than controls with other neurological disorders. A random effects model of 30 cohorts found that an estimated 55% (95% CI 46% to 64%) of 4272 patients with FND reported pain. Random effects models estimated diagnoses of complex regional pain syndrome in 22% (95% CI 6% to 39%) of patients, irritable bowel syndrome in 16% (95% CI 9% to 24%) and fibromyalgia in 10% (95% CI 8% to 13%). Five studies of FND diagnoses among 361 patients with chronic pain were identified. Most interventions for FND did not ameliorate pain, even when other symptoms improved. CONCLUSIONS: Pain symptoms and pain-related diagnoses are common in FND. Classification systems and treatments should routinely consider pain as a comorbidity in patients with FND.

What is brain fog?

BACKGROUND: The term 'brain fog' is increasingly used colloquially to describe difficulties in the cognitive realm. But what is brain fog? What sort of experiences do people talk about when they talk about brain fog? And, in turn, what might this tell us about potential underlying pathophysiological mechanisms? This study examined first-person descriptions in order to better understand the phenomenology of brain fog. METHODS: Posts containing 'brain fog' were scraped from the social media platform Reddit, using python, over a week in October 2021. We examined descriptions of brain fog, themes of containing subreddits (topic-specific discussion forums), and causal attributions. RESULTS: 1663 posts containing 'brain fog' were identified, 717 meeting inclusion criteria. 141 first person phenomenological descriptions depicted forgetfulness (51), difficulty concentrating (43), dissociative phenomena (34), cognitive 'slowness' and excessive effort (26), communication difficulties (22), 'fuzziness' or pressure (10) and fatigue (9). 50% (363/717) posts were in subreddits concerned with illness and disease: including COVID-19 (87), psychiatric, neurodevelopmental, autoimmune and functional disorders. 134 posts were in subreddits about drug use or discontinuation, and 44 in subreddits about abstention from masturbation. 570 posts included the poster's causal attribution, the most frequent attribution being long COVID in 60/570 (10%). CONCLUSIONS: 'Brain fog' is used on Reddit to describe heterogeneous experiences, including of dissociation, fatigue, forgetfulness and excessive cognitive effort, and in association with a range of illnesses, drugs and behaviours. Encouraging detailed description of these experiences will help us better understand pathophysiological mechanisms underlying cognitive symptoms in health and disease.

Anomalies in the review process and interpretation of the evidence in the NICE guideline for chronic fatigue syndrome and myalgic encephalomyelitis.

Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is a disabling long-term condition of unknown cause. The National Institute for Health and Care Excellence (NICE) published a guideline in 2021 that highlighted the seriousness of the condition, but also recommended that graded exercise therapy (GET) should not be used and cognitive-behavioural therapy should only be used to manage symptoms and reduce distress, not to aid recovery. This U-turn in recommendations from the previous 2007 guideline is controversial.We suggest that the controversy stems from anomalies in both processing and interpretation of the evidence by the NICE committee. The committee: (1) created a new definition of CFS/ME, which 'downgraded' the certainty of trial evidence; (2) omitted data from standard trial end points used to assess efficacy; (3) discounted trial data when assessing treatment harm in favour of lower quality surveys and qualitative studies; (4) minimised the importance of fatigue as an outcome; (5) did not use accepted practices to synthesise trial evidence adequately using GRADE (Grading of Recommendations, Assessment, Development and Evaluations trial evidence); (6) interpreted GET as mandating fixed increments of change when trials defined it as collaborative, negotiated and symptom dependent; (7) deviated from NICE recommendations of rehabilitation for related conditions, such as chronic primary pain and (8) recommended an energy management approach in the absence of supportive research evidence.We conclude that the dissonance between this and the previous guideline was the result of deviating from usual scientific standards of the NICE process. The consequences of this are that patients may be denied helpful treatments and therefore risk persistent ill health and disability.

Functional neurological disorder is a feminist issue.

Functional neurological disorder (FND) is a common and disabling disorder, often misunderstood by clinicians. Although viewed sceptically by some, FND is a diagnosis that can be made accurately, based on positive clinical signs, with clinical features that have remained stable for over 100 years. Despite some progress in the last decade, people with FND continue to suffer subtle and overt forms of discrimination by clinicians, researchers and the public. There is abundant evidence that disorders perceived as primarily affecting women are neglected in healthcare and medical research, and the course of FND mirrors this neglect. We outline the reasons why FND is a feminist issue, incorporating historical and contemporary clinical, research and social perspectives. We call for parity for FND in medical education, research and clinical service development so that people affected by FND can receive the care they need.

Functional neurological disorder is common in patients attending chronic pain clinics.

BACKGROUND AND PURPOSE: Chronic pain is a common comorbidity in those with functional neurological disorder (FND); however, the prevalence and characteristics of FND in those with chronic pain is unknown. METHODS: A retrospective electronic records review was made of consecutive new patients attending a chronic pain clinic of a regional service. Clinical features, medication for and outcome of chronic pain, any lifetime diagnoses of functional disorders, FND, and psychiatric disorders, and undiagnosed neurological symptoms were recorded. RESULTS: Of 190 patients attending the chronic pain clinic, 32 (17%) had a lifetime diagnosis of FND and an additional 11 (6%) had undiagnosed neurological symptoms. Pain patients with comorbid FND were more likely to have chronic primary pain (88% with FND, 44% without FND, p < 0.0001), widespread chronic primary pain (53%, 15%, p < 0.00001), and depression (84%, 52%, p < 0.005) and less likely to have a pain-precipitating event (19% vs. 56%, p < 0.001). However, there was no significant difference between these patients in opiate prescription, benzodiazepine prescription, or pain outcome. CONCLUSIONS: This first study of FND in a chronic pain patient population found a remarkably high prevalence of FND (17%) and is possibly an underestimation. The size of the overlap indicates that FND and chronic pain research fields are likely to have a lot to learn from each other.

Functional neurological disorder: A common reason for a neurology inpatient referral.

BACKGROUND AND PURPOSE: In 2021, the European Academy of Neurology's training requirements were updated to include functional neurological disorder (FND) as a core topic for the first time. To reinforce these changes, we aimed to understand the proportion of inpatients (in non-neurology settings) who are diagnosed with FND. METHODS: We prospectively collected data on diagnoses made after inpatient ward reviews from neurology trainees at three tertiary neurology centres in Scotland from April to September 2021. We assessed healthcare utilization data for patients with a diagnosis of FND, epilepsy and epileptic seizures, or a neuroinflammatory disorder over the preceding 12 months. RESULTS: There were 437 inpatient reviews for 424 patients by 13 trainees. The largest single diagnosis was FND (n = 80, 18%), followed by epilepsy (n = 64, 14%), primary headache disorder (n = 40, 9%) and neuroinflammatory disorders (n = 28, 6%). There was an uncertain diagnosis for 48 reviews (11%). Compared to patients with epilepsy or neuroinflammatory disorders, patients with FND had a similar number of admissions (2 vs. 2 vs. 1) and brain/spine imaging studies (2 vs. 1 vs. 2). CONCLUSIONS: In Scotland, FND was the most common diagnosis made after a request for an inpatient review by a neurologist from another department in the hospital. Patients with FND have similar health resource needs to those with other common neurological disorders when they present to hospitals with tertiary neurology centres. This data supports the inclusion of FND as a core curriculum topic in neurology training.

Diagnosis of cauda equina syndrome in the emergency department.

Cauda equina syndrome (CES) is a spinal emergency that can be challenging to identify from among the many patients presenting to EDs with low back and/or radicular leg pain. This article presents a practical guide to the assessment and early management of patients with suspected CES as well as an up-to-date review of the most important studies in this area that should inform clinical practice in the ED.

Demographics of Cauda Equina Syndrome: A Population-Based Incidence Study.

INTRODUCTION: Cauda equina syndrome (CES) has significant medical, social, and legal consequences. Understanding the number of people presenting with CES and their demographic features is essential for planning healthcare services to ensure timely and appropriate management. We aimed to establish the incidence of CES in a single country and stratify incidence by age, gender, and socioeconomic status. As no consensus clinical definition of CES exists, we compared incidence using different diagnostic criteria. METHODS: All patients presenting with radiological compression of the cauda equina due to degenerative disc disease and clinical CES requiring emergency surgical decompression during a 1-year period were identified at all centres performing emergency spinal surgery across Scotland. Initial patient identification occurred during the emergency hospital admission, and case ascertainment was checked using ICD-10 diagnostic coding. Clinical information was reviewed, and incidence rates for all demographic and clinical groups were calculated. RESULTS: We identified 149 patients with CES in 1 year from a total population of 5.4 million, giving a crude incidence of 2.7 (95% CI: 2.3-3.2) per 100,000 per year. CES occurred more commonly in females and in the 30-49 years age range, with an incidence per year of 7.2 (95% CI: 4.7-10.6) per 100,000 females age 30-39. There was no association between CES and socioeconomic status. CES requiring catheterization had an incidence of 1.1 (95% CI: 0.8-1.5) per 100,000 adults per year. The use of ICD-10 codes alone to identify cases gave much higher incidence rates, but was inaccurate, with 55% (117/211) of patients with a new ICD-10 code for CES found not to have CES on clinical notes review. CONCLUSION: CES occurred more commonly in females and in those between 30 and 49 years and had no association with socioeconomic status. The incidence of CES in Scotland is at least four times higher than previous European estimates of 0.3-0.6 per 100,000 population per year. Incidence varies with clinical diagnostic criteria. To enable comparison of rates of CES across populations, we recommend using standardized clinical and radiological criteria and standardization for population structure.

'Scan-negative' cauda equina syndrome: what to do when there is no neurosurgical cause.

Suspected cauda equina syndrome is a common presentation in emergency departments, but most patients (≥70%) have no cauda equina compression on imaging. As neurologists become more involved with 'front door' neurology, referral rates of patients with these symptoms are increasing. A small proportion of patients without structural pathology have other neurological causes: we discuss the differential diagnosis and how to recognise these. New data on the clinical features of patients with 'scan-negative' cauda equina syndrome suggest that the symptoms are usually triggered by acute pain (with or without root impingement) causing changes in brain-bladder feedback in vulnerable individuals, exacerbated by medication and anxiety, and commonly presenting with features of functional neurological disorder.

Testing the 'seizure scaffold': What can experimental simulation tell us about functional seizures?

INTRODUCTION: It has been suggested for over 100 years that patterns of neurological symptoms and signs in functional neurological disorders may be shaped at a neural level by underlying ideas or preconceptions how neurological symptoms present. This study used experimental simulation to probe ideas about seizures in healthy volunteers, with a view to compare with features commonly observed in functional and epileptic seizure disorders. METHODS: Sixty healthy volunteers were instructed to simulate an epileptic seizure. The episodes were video-recorded and assessed by three qualified markers for the presence of clinical features commonly observed in functional seizures (FS), epileptic seizures, and syncope. RESULTS: Simulated seizures were hyperkinetic (83%), hypokinetic (7%), or staring (10%). Fifty-two percent had their eyes open and 45% eyes closed. Tremor was observed in 70%, while clonic jerking was only present in 17%. The majority of volunteers maintained a normal or floppy body posture. Head shaking side-to-side was observed in 38%, while guttural cries, stertorous breathing, tearfulness, and hyperventilation were absent in all volunteers. DISCUSSION: Our results suggest that simulated seizures not only resemble FS more closely than epileptic seizures but also show some important differences. Subjective seizure experiences in people with FS, not captured by this experimental simulation, remain a core determinant of semiology.

Are we neglecting sexual function assessment in suspected cauda equina syndrome?

OBJECTIVES: We assessed the documentation rates of signs and symptoms, including sexual function, in patients with suspected cauda equina syndrome and whether they can be improved by increasing local awareness. PATIENTS AND METHODS: We reviewed all electronic records of patients referred with suspected CES who required urgent MRI to our regional service over a 2 month period. We recorded the documentation rates of clinical signs and symptoms. The results were presented locally to increase awareness. A further 2 month period was then re-audited. 120 patients in total were included across both time periods. Chi-squared was used to compare documentation rates between time periods. RESULTS: 25 of 120 patients had radiological cauda equina compression. Lower limb neurology, urinary function and saddle sensation were almost universally documented. After the intervention, there was a significant increase (p < 0.05) in the documentation of bowel function and post-void residual but not sexual function. Sexual function was poorly documented with rates of 3% and 11% throughout the two audited periods. CONCLUSION: Certain clinical features of CES are well documented. Increasing awareness may improve documentation of certain symptoms/signs in patients with suspected cauda equina syndrome. Sexual function was poorly documented and increasing awareness alone is an inadequate intervention.

Does a history of lumbar spine surgery predict radiological cauda equina compression in patients undergoing MRI for suspected cauda equina syndrome?

Background: The clinical symptoms and signs of Cauda equina syndrome (CES) are non specific and poorly predictive of cauda equina compression on MRI. We aimed to establish whether a history of lumbar spine surgery predicts cauda equina compression on MRI in those presenting with suspected CES.Methods: A retrospective electronic record review was undertaken of 276 patients referred with clinically suspected CES who underwent a lumbosacral spine MRI. Those with a history of prior lumbar surgery were compared to those without. The likelihood of cauda equina compression was compared between the two groups.Results: About 78/276 (28%) patients with suspected CES had radiological compression of the cauda equina and went on to surgical decompression. A total of 54 (20%) patients had undergone prior lumbar surgery. Patients with a history of lumbar surgery were less likely to have cauda equina compression on MRI (χ2 - p = .035). Twenty six (9%) patients presented more than once with suspected CES. Patients with a history of lumbar surgery were more likely to re-present with suspected CES (χ2 - p = .002).Conclusions: Prior lumbar surgery was associated with a higher frequency of re-presentation with clinically suspected CES but a lower frequency of radiological cauda equina compression.

Complex regional pain syndrome and functional neurological disorders - time for reconciliation.

There have been many articles highlighting differences and similarities between complex regional pain syndrome (CRPS) and functional neurological disorders (FND) but until now the discussions have often been adversarial with an erroneous focus on malingering and a view of FND as 'all in the mind'. However, understanding of the nature, frequency and treatment of FND has changed dramatically in the last 10-15 years. FND is no longer assumed to be only the result of 'conversion' of psychological conflict but is understood as a complex interplay between physiological stimulus, expectation, learning and attention mediated through a Bayesian framework, with biopsychosocial predisposing, triggering and perpetuating inputs. Building on this new 'whole brain' perspective of FND, we reframe the debate about the 'psychological versus physical' basis of CRPS. We recognise how CRPS research may inform mechanistic understanding of FND and conversely, how advances in FND, especially treatment, have implications for improving understanding and management of CRPS.

Understanding foreign accent syndrome.

OBJECTIVE: Foreign accent syndrome (FAS) is widely understood as an unusual consequence of structural neurological damage, but may sometimes represent a functional neurological disorder. This observational study aimed to assess the prevalence and utility of positive features of functional FAS in a large group of individuals reporting FAS. METHODS: Participants self-reporting FAS recruited from informal unmoderated online support forums and via professional networks completed an online survey. Speech samples were analysed in a subgroup. RESULTS: Forty-nine respondents (24 UK, 23 North America, 2 Australia) reported FAS of mean duration 3 years (range 2 months to 18 years). Common triggers were: migraine/severe headache (15), stroke (12), surgery or injury to mouth or face (6) and seizure (5, including 3 non-epileptic). High levels of comorbidity included migraine (33), irritable bowel syndrome (17), functional neurological disorder (12) and chronic pain (12). Five reported structural lesions on imaging. Author consensus on aetiology divided into, 'probably functional (n=35.71%), 'possibly structural' (n=4.8%) and 'probably structural' (n=10.20%), but positive features of functional FAS were present in all groups. Blinded analysis of speech recordings supplied by 13 respondents correctly categorised 11 (85%) on the basis of probable aetiology (functional vs structural) in agreement with case history assignment. CONCLUSIONS: This largest case series to date details the experience of individuals with self-reported FAS. Although conclusions are limited by the recruitment methods, high levels of functional disorder comorbidity, symptom variability and additional linguistic and behavioural features suggest that chronic FAS may in some cases represent a functional neurological disorder, even when a structural lesion is present.

Evaluation of nationwide referral pathways, investigation and treatment of suspected cauda equina syndrome in the United Kingdom.

Purpose: Cauda equina syndrome (CES) is a spinal emergency with clinical symptoms and signs that have low diagnostic accuracy. National guidelines in the United Kingdom (UK) state that all patients should undergo an MRI prior to referral to specialist spinal units and surgery should be performed at the earliest opportunity. We aimed to evaluate the current practice of investigating and treating suspected CES in the UK. Materials and Methods: A retrospective, multicentre observational study of the investigation and management of patients with suspected CES was conducted across the UK, including all patients referred to a spinal unit over 6 months between 1st October 2016 and 31st March 2017. Results: A total of 28 UK spinal units submitted data on 4441 referrals. Over half of referrals were made without any previous imaging (n = 2572, 57.9%). Of all referrals, 695 underwent surgical decompression (15.6%). The majority of referrals were made out-of-hours (n = 2229/3517, 63.4%). Patient location and pre-referral imaging were not associated with time intervals from symptom onset or presentation to decompression. Patients investigated outside of the spinal unit experienced longer time intervals from referral to undergoing the MRI scan. Conclusions: This is the largest known study of the investigation and management of suspected CES. We found that the majority of referrals were made without adequate investigations. Most patients were referred out-of-hours and many were transferred for an MRI without subsequently requiring surgery. Adherence to guidelines would reduce the number of referrals to spinal services by 72% and reduce the number of patient transfers by 79%.

'Cryptogenic Drop Attacks' revisited: evidence of overlap with functional neurological disorder.

OBJECTIVE: In their 1973 BMJ paper 'Cryptogenic Drop Attacks', Stevens and Matthews described 40, mostly middle-aged, female patients with drop attacks of unknown cause. Although clinically common, there has been little on this topic since. We aimed to determine clinical features, comorbidity and outcome of patients with drop attacks. METHODS: We carried out a retrospective review of patients with cryptogenic drop attacks seen consecutively by one clinician (JS) between 2006 and 2016. Demographics, phenomenology, duration and frequency of attacks, attack description and comorbid diagnoses were recorded. Patients were followed up with a notes review. RESULTS: 83 patients with cryptogenic drop attacks were predominantly female (89%, n=79), mean age 44 years. The majority (93%, n=77) could not remember the fall itself and almost half (43%, n=36) experienced prodromal dissociative symptoms. Mechanical trips or syncope preceded drop attacks, historically, in 24% (n=20) of cases. Persistent fatigue (73%, n=61), chronic pain (40%, n=33), functional limb weakness (31%,n=26) and dissociative (non-epileptic) attacks 28% (n=23) were common, with the latter usually preceding or emerging from drop attacks. At follow-up (88%, mean 38 months), 28% (n=23) had resolution of their drop attacks. Predisposing (but non-causative) disease comorbidity was found at baseline (n=12) and follow-up (n=5). CONCLUSIONS: Cryptogenic drop attacks are associated with high frequency of comorbid functional somatic and functional neurological disorders. Patients commonly have prodromal dissociative symptoms and in some there was a clear relationship with prior or subsequent dissociative (non-epileptic) attacks. Some cryptogenic drop attacks may be best understood as phenomena on the spectrum of dissociative attacks.

Fowler's syndrome of urinary retention: A retrospective study of co-morbidity.

AIMS: To study the frequency of pain, psychological, or functional disorders in patients with Fowler's syndrome. METHODS: We carried out a retrospective chart review of patients with a diagnosis of Fowler's syndrome attending the Uro-Neurology centre at the National Hospital for Neurology and Neurosurgery between 2009 and 2013 looking at triggering events, physical and psychological comorbidities. RESULTS: Of 62 patients with clinical and electromyographic diagnosis of Fowler's syndrome, 31 (50%) had unexplained chronic pain syndromes, 12 (19%) of these were taking opiates. Fifteen (24%) had "functional" neurological symptoms. Abdominopelvic surgery with general anesthesia was the leading trigger (n = 21, 35%). CONCLUSIONS: We found high levels of co-morbidity with patients having some form of pain (50%), a probable functional disorder (24%), or psychological symptoms (31%). There are several potential explanations for this association including the effect of developing an apparently unexplained distressing condition, confounding effect of opiate use or referral bias. The findings suggest a need for prospective systematic study of comorbidity for this disabling condition. Neurourol. Urodynam. 35:601-603, 2016. © 2015 Wiley Periodicals, Inc.

'Scan-negative' cauda equina syndrome: Evidence of functional disorder from a prospective case series.

In the first prospective comparison of 'scan-negative' (n=11) and 'scan-positive' (n=7) patients with cauda equina syndrome (CES) we found that Hoover's sign of functional leg weakness but not routine clinical features differentiated the two groups (p<0.02). This offers a new direction of study in this area, although magnetic resonance imaging is still required for all patients with possible CES.

Chronic idiopathic urinary retention: Comorbidity and outcome in 102 individuals.

OBJECTIVES: Chronic Idiopathic urinary retention is poorly understood. One small study suggests higher than expected rates of functional neurological disorder and pain comorbidity which may have implications for understanding the disorder. We investigated the frequency of functional neurological disorder, chronic pain other medical and psychiatric comorbidity, triggers of urinary retention, results of urodynamic assessment, medication history, management, and outcome in patients with chronic idiopathic urinary retention. METHODS: A consecutive retrospective electronic notes analysis was undertaken of patients with chronic idiopathic urinary retention presenting to a secondary care urology clinic between Jan 2018-Jan 2021, with follow-up to their most recent urological appointment. RESULTS: 102 patients were identified (mean age of 41.9 years, 98% female). 25% had functional neurological disorder (n = 26), most commonly limb weakness (n = 19, 19%) and functional seizures (n = 16, 16%). Chronic pain (n = 58, 57%) was a common comorbidity. Surgical and medical riggers to urinary retention were found in almost half of patients (n = 49, 48%). 81% of patients underwent urodynamic assessment (n = 83). Most frequently no specific abnormality was reported (n = 30, 29%). Hypertonic urethral sphincter was the most identified urodynamic abnormality (n = 17, 17%). We noted high levels of opioid (n = 50, 49%) and benzodiazepine (n = 27, 26%) use. Urinary retention resolved in only a small number of patients (n = 6, 6%, median follow up 54 months), in three cases spontaneously. CONCLUSION: This preliminary data suggests idiopathic urinary retention is commonly comorbid with functional neurological disorder, and chronic pain, suggesting shared mechanisms.

Cauda equina syndrome.

Aims: Patients with cauda equina syndrome (CES) require emergency imaging and surgical decompression. The severity and type of symptoms may influence the timing of imaging and surgery, and help predict the patient's prognosis. Categories of CES attempt to group patients for management and prognostication purposes. We aimed in this study to assess the inter-rater reliability of dividing patients with CES into categories to assess whether they can be reliably applied in clinical practice and in research. Methods: A literature review was undertaken to identify published descriptions of categories of CES. A total of 100 real anonymized clinical vignettes of patients diagnosed with CES from the Understanding Cauda Equina Syndrome (UCES) study were reviewed by consultant spinal surgeons, neurosurgical registrars, and medical students. All were provided with published category definitions and asked to decide whether each patient had 'suspected CES'; 'early CES'; 'incomplete CES'; or 'CES with urinary retention'. Inter-rater agreement was assessed for all categories, for all raters, and for each group of raters using Fleiss's kappa. Results: Each of the 100 participants were rated by four medical students, five neurosurgical registrars, and four consultant spinal surgeons. No groups achieved reasonable inter-rater agreement for any of the categories. CES with retention versus all other categories had the highest inter-rater agreement (kappa 0.34 (95% confidence interval 0.27 to 0.31); minimal agreement). There was no improvement in inter-rater agreement with clinical experience. Across all categories, registrars agreed with each other most often (kappa 0.41), followed by medical students (kappa 0.39). Consultant spinal surgeons had the lowest inter-rater agreement (kappa 0.17). Conclusion: Inter-rater agreement for categorizing CES is low among clinicians who regularly manage these patients. CES categories should be used with caution in clinical practice and research studies, as groups may be heterogenous and not comparable.