Risk factors for development and persistence of chronic widespread pain in spondyloarthritis: a population-based two-year follow-up study

Nociplastic pain in axial spondyloarthritis and psoriatic arthritis: role of JAK kinases in Immunopathology and therapeutic impact of JAK inhibitors

INTRODUCTION

Pain in both peripheral and axial joints is a major symptom in patients with psoriatic arthritis (PsA) and axial spondyloarthritis (axSpA). Emerging evidence demonstrates pain mechanisms, beyond those related to inflammation or joint damage, based on aberrant processing of nociceptive stimuli peripherally as well as centrally. The Janus kinase/signal transducers and activators of transcription (JAK-STAT) signaling pathway has been implicated in the processing of pain beyond its role in mediating inflammation and inhibitors of this pathway approved for the treatment of axSpA and PsA have been shown to alleviate a broad array of pain outcomes in both axial and peripheral joints.

AREAS COVERED

We review recent definitions and standardization of the nomenclature for categorizing chronic pain according to causality, assessment tools to evaluate nociplastic pain, the pathophysiologic role of JAK-STAT signaling in nociplastic pain, evidence for the presence of nociplastic pain in axSpA and PsA, and the impact of JAK inhibitors (JAKi) on pain outcomes in clinical trials (PubMed: 01/01/2019-04/01-2024).

EXPERT OPINION

Nociplastic pain assessment has been confined almost entirely to the use of a limited number of questionnaires in cross-sectional studies of these diseases. Though effective for alleviating pain, it is unclear if JAKi specifically impact nociplastic pain.

Pain in axial spondyloarthritis: role of the JAK/STAT pathway

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that is characterized by new bone formation in the axial musculoskeletal system, with X-ray discriminating between radiographic and non-radiographic forms. Current therapeutic options include non-steroidal anti-inflammatory drugs in addition to biological disease-modifying anti-rheumatic drugs that specifically target tumor necrosis factor-alpha (TNFα) or interleukin (IL)-17. Pain is the most critical symptom for axSpA patients, significantly contributing to the burden of disease and impacting daily life. While the inflammatory process exerts a major role in determining pain in the early phases of the disease, the symptom may also result from mechanical and neuromuscular causes that require complex, multi-faceted pharmacologic and non-pharmacologic treatment, especially in the later phases. In clinical practice, pain often persists and does not respond further despite the absence of inflammatory disease activity. Cytokines involved in axSpA pathogenesis interact directly/indirectly with the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling cascade, a fundamental component in the origin and development of spondyloarthropathies. The JAK/STAT pathway also plays an important role in nociception, and new-generation JAK inhibitors have demonstrated rapid pain relief. We provide a comprehensive review of the different pain types observed in axSpA and the potential role of JAK/STAT signaling in this context, with specific focus on data from preclinical studies and data from clinical trials with JAK inhibitors.

Sex-specific diagnostic efficacy of MRI in axial spondyloarthritis: challenging the 'One Size Fits All' notion

OBJECTIVES

Sex-specific differences in the presentation of axial spondyloarthritis (axSpA) may contribute to a diagnostic delay in women. The aim of this study was to investigate the diagnostic performance of MRI findings comparing men and women.

METHODS

Patients with back pain from six different prospective cohorts (n=1194) were screened for inclusion in this post hoc analysis. Two blinded readers scored the MRI data sets independently for the presence of ankylosis, erosion, sclerosis, fat metaplasia and bone marrow oedema. Χ2 tests were performed to compare lesion frequencies. Contingency tables were used to calculate markers for diagnostic performance, with clinical diagnosis as the standard of reference. The positive and negative likelihood ratios (LR+/LR-) were used to calculate the diagnostic OR (DOR) to assess the diagnostic performance.

RESULTS

After application of exclusion criteria, 526 patients (379 axSpA (136 women and 243 men) and 147 controls with chronic low back pain) were included. No major sex-specific differences in the diagnostic performance were shown for bone marrow oedema (DOR m: 3.0; f: 3.9). Fat metaplasia showed a better diagnostic performance in men (DOR 37.9) than in women (DOR 5.0). Lower specificity was seen in women for erosions (77% vs 87%), sclerosis (44% vs 66%), fat metaplasia (87% vs 96%).

CONCLUSION

The diagnostic performance of structural MRI markers is substantially lower in female patients with axSpA; active inflammatory lesions show comparable performance in both sexes, while still overall inferior to structural markers. This leads to a comparably higher risk of false positive findings in women.

The natural history of chronic widespread pain in patients with axial spondyloarthritis: a cohort study with clinical and self-tracking data

OBJECTIVES

This study investigates longitudinal patterns, predictors and long-term impact of pain in axial spondyloarthritis (axSpA), using clinical and self-tracking data.

METHODS

The presence of multisite pain (MSP), affecting at least six of nine body regions using a Margolis pain drawing, and subsequent chronic widespread pain (CWP), MSP at more than one timepoint, was assessed in a cohort of axSpA patients. Incident MSP (MSP at two consecutive visits or more), intermittent MSP (MSP at two or more non-consecutive visits) and persistent MSP (MSP at each visit) were described. Demographic, clinical and self-tracking measures were compared for the CWP vs non-CWP groups using Students t test, Wilcoxon-Mann-Whitney and χ2 test for normal, non-normal and categorical data, respectively. Predictors of CWP were evaluated using logistic regression modelling.

RESULTS

A total of 136 patients, mean clinical study duration of 120 weeks (range 27-277 weeks) were included, with sufficient self-tracking data in 97 patients. Sixty-eight (50%) patients reported MSP during at least one clinical visit: eight (6%) incident MSP; 16 (12%) persistent MSP; and 44 (32%) intermittent MSP. Forty-six (34%) of the cohort had CWP. All baseline measures of disease activity, function, quality of life, sleep disturbance, fatigue and overall activity impairment were significant predictors of the development of CWP. BASDAI and BASFI scores were significantly higher in those with CWP and self-tracking data revealed significantly worse pain, fatigue, sleep quality and stress.

CONCLUSIONS

The development of CWP is predicted by higher levels of disease activity and burden at baseline. It also impacts future disease activity and wellbeing.

The effect of central sensitization on disease activity measures, quality of life and clinical parameters in axial spondyloarthritis: a cross-sectional study

Objective

Despite biological drug therapy, pain remains a persistent complaint in patients with axial spondyloarthritis (axSpA). We aimed to investigate the effect of central sensitization (CS) on disease activity measures, quality of life, and clinical parameters in axSpA patients.

Methods

We consecutively recruited axSpA patients who were followed up at our rheumatology outpatient clinic, and age- and sex-matched controls in this cross-sectional study. The central sensitization inventory, douleur neuropathique 4 (DN4) questions, and 2010 American College of Rheumatology fibromyalgia (FM) diagnostic criteria were applied to all individuals. The patients' clinical parameters were recorded. The data of the patient and control groups were compared.

Results

Of the 116 axSpA patients (57 female) and 95 controls (46 female) who participated in this study, CS was determined in 46.6% of axSpA patients and 13.7% of controls (p<0.001). Patients with CS exhibited high disease activity, and poor quality of life and functionality than without it (all p<0.001). The median CS, frequency of FM and frequency of neuropathic pain were higher in patients than in the controls (all p<0.001). CS-related conditions, including anxiety and depression, were higher in axSpA patients than in controls (both p<0.05).

Conclusion

The results showed that CS was common in axSpA patients, and patients with CS had higher disease activity, worse quality of life, and worse functional status than those without CS.

Mechanisms of chronic pain in inflammatory rheumatism: the role of descending modulation

ABSTRACT

Persistent pain despite satisfactory disease treatment is frequent in rheumatoid arthritis (RA) and spondyloarthritis (Spa) and may result from specific changes in central pain processing. We assessed these mechanisms further by systematically comparing thermal pain thresholds and conditioned pain modulation (CPM) between patients with active RA or Spa and healthy controls. We included 50 patients with RA and 50 patients with Spa and 100 age-matched and sex-matched controls. Heat and cold pain thresholds (HPT-CPT) were measured on the dominant forearm, and CPM was assessed by applying conditioning stimuli (immersion in a cold-water bath) to one foot and the nondominant hand in 2 successive randomized sequences. Descending pain modulation was assessed as the difference in HPTs (in °C) before and after conditioning. Larger HPT differences (ie, a larger CPM effect) reflected more efficient descending inhibition. Potential associations between changes in CPM and clinical data, including disease activity, pain intensity, and psychological and functional variables, were systematically assessed. Heat pain threshold and cold pain threshold were similar in patients and controls. The mean CPM effect was significantly weaker in patients than that in controls for conditioning applied to either the foot (0.25°C ±2.57 vs 2.79°C ±2.31; P < 0.001) or the nondominant hand (0.57°C ±2.74 vs 2.68°C ±2.12; P < 0.001). The smaller CPM effect in patients was correlated with average pain intensity, but not with disease activity or other clinical characteristics, suggesting a significant pathophysiological role for changes in endogenous pain modulation in the mechanisms of chronic pain associated with inflammatory rheumatism.

Sex Disparities of the Sacroiliac Joint: Focus on Joint Anatomy and Imaging Appearance

The sacroiliac joint (SIJ) is an anatomically complex joint which, as a functional unit with the pelvis and spine, is of decisive biomechanical importance for the human body. It is also a commonly overlooked source of lower back pain. Like the entire bony pelvis, the SIJ exhibits major sexual dimorphisms; thus, the sex-dependent evaluation of this joint is becoming increasingly important in clinical practice, both anatomically with joint shape variations and biomechanical differences as well as in terms of image appearance. The influence of the SIJ shape, which differs in women and men, is crucial for the different biomechanical joint properties. These differences are important in the development of joint diseases at the SIJ, which shows a specific difference between the sexes. This article aims to provide an overview of sex disparities of the SIJ regarding different anatomical and imaging appearances to further understand the insights into the interplay of sex differences and SIJ disease.

Association between depression, anxiety, chronic pain, or opioid use and tumor necrosis factor inhibitor persistence in inflammatory arthritis

INTRODUCTION

Depression, anxiety, and chronic pain are common comorbidities in patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA), and ankylosing spondylitis (AS) and may substantially impact patient outcomes. We aimed to determine whether these comorbidities were associated with earlier TNF-inhibitor (TNFi) discontinuation.

METHODS

This retrospective cohort study using Optum's de-identified Clinformatics® Data Mart Database 2000-2014 identified patients with RA, PsA, and AS initiating a first TNFi. Depression/anxiety, chronic pain, and opioid use were identified using diagnosis codes and prescription fill data. Cox proportional hazards models were used to compare time to medication discontinuation in patients with or without each of these risk factors and to assess the additive effect of having multiple risk factors.

RESULTS

Among 33,744 patients initiating a TNFi (23,888 RA, 6443 PsA, 3413 AS), depression/anxiety, chronic pain, and opioid use were common, with ≥ 1 risk factor in 48.1%, 42.5%, and 55.4% of patients with RA, PsA, and AS respectively. Each risk factor individually was associated with a 5-7-month lower median treatment persistence in each disease (all p < 0.001). Presence of multiple risk factors had an additive effect on time to discontinuation with HR (95% CI) 1.19 (1.14-1.24), 1.41 (1.33-1.49), and 1.47 (1.43-1.73) for 1, 2, or 3 risk factors respectively in RA. Findings were similar in PsA and AS.

CONCLUSIONS

Depression, anxiety, chronic pain, and opioid use are common in inflammatory arthritis and associated with earlier TNFi discontinuation. Recognizing and managing these risk factors may improve treatment persistence, patient outcomes, and cost of care. Key Points • Depression, anxiety, chronic pain, and opioid use are common in patients with inflammatory arthritis. • In patients initiating treatment with a TNF-inhibitor, depression, anxiety, chronic pain, or recent opioid use are associated with sooner discontinuation of TNFi therapy. • Patients with multiple of these risk factors are even more likely to discontinue therapy sooner.

Sex-associated and gender-associated differences in the diagnosis and management of axial spondyloarthritis: addressing the unmet needs of female patients

Emerging evidence suggests that axial spondyloarthritis (axSpA) should not be seen as a predominantly male disease, as the non-radiographic form occurs with roughly equal frequency in women and men. However, men and women experience this disease differently. The purpose of this review is to highlight sex-associated and gender-associated differences in the patient's journey through the diagnosis and management of axSpA, in order to increase the awareness about the unmet needs of female axSpA patients.Female patients experience a longer diagnostic delay compared with men, possibly due to the different pattern of clinical presentations across genders. Therefore, it is crucial to sensitise physicians to pay attention and identify the red flags of axSpA in women and promote early referral to a rheumatologist. Women with a diagnosis of axSpA experience greater limitations in physical function, although they have less structural spinal damage compared with men. Women tend to have less adherence and a lower response to treatment, so more gender-oriented data are needed about drugs used for axSpA, especially biological disease-modifying antirheumatic drugs.Lifestyle factors have a strong impact on the disease course. Interventions regarding physical activity, smoking cessation and diet should be communicated to the patients, with particular attention to the gender-related cultural background.Patients of childbearing age living with axSpA should be engaged in a discussion about reproductive health, in terms of preservation of fertility, management of pregnancy and delivery and use of biologic drugs during pregnancy and breastfeeding.

Disease activity in women with ankylosing spondylitis remains higher under Tumour Necrosis Factor inhibitor treatment than in men: a five-year observational study

OBJECTIVE

To assess sex differences in response, level of disease activity, and drug survival in tumour necrosis factor inhibitor (TNFi)-naïve ankylosing spondylitis (AS) patients.

METHOD

Consecutive AS patients, fulfilling the modified New York criteria, were included in a prospective cohort study at initiation of the first TNFi and followed until this medication was stopped (drug survival). Disease activity scores [AS Disease Activity Score using C-reactive protein (ASDAS-CRP), Bath AS Disease Activity Index (BASDAI), and CRP] were measured at 3, 6, and 12 months, and every subsequent year, up to 5 years. The response was defined by the ASDAS-CRP response criteria (clinically important improvement: ASDAS-CRP decrease ≥ 1.1). Analyses included regression methods for repeated measurements and survival analyses.

RESULTS

Overall, 356 patients were included (34% women, mean ± sd age 46 ± 12 years), with a median disease duration of 12 (interquartile range 6;20) years. Women were less likely than men to achieve a clinically important response after 6 months of TNFi treatment (47% vs 64%; relative risk 1.4, 95% confidence interval (CI) 1.1;1.9, p = 0.02], despite a lack of sex differences in mean ASDAS-CRP levels over 5 year follow-up. Adjusted models for BASDAI over 5 years showed that women had a 0.6 point higher BASDAI score than men (β = 0.6 0.1;1.1 <0.02). Numerically, more women than men discontinued treatment over a period of 5 years (hazard ratio = 1.5, 95% CI 0.9;2.5, p = 0.15).

CONCLUSION

Female AS patients show a lower response to TNFi and a higher disease activity compared to men.

Pain in rheumatoid arthritis: a seven-year follow-up study of pain distribution and factors associated with transition from and to chronic widespread pain

Objective: To study transitions from and to chronic widespread pain (CWP) over 7 years in patients with rheumatoid arthritis (RA).Method: Two postal questionnaires were sent to patients included in the BARFOT (Better Anti-Rheumatic Pharmacotherapy) study, the first in 2010 and the second in 2017. The questionnaires assessed pain, number of tender and swollen joints, functional disability, health-related quality of life (HRQoL), pharmacological treatment, lifestyle factors, and patient-reported body mass index (BMI). The responders to both questionnaires were divided into three groups according to the reported pain duration and distribution: patients having no chronic pain (NCP), chronic regional pain (CRP), and CWP.Results: In all, 953 patients answered the questionnaires at both time-points. One-third (324) of the patients reported CWP in 2010, and 140 (43%) of the patients had transition to NCP or CRP in 2017. In multivariate logistic regression models, adjusting for age, gender, and disease duration, transition from CWP was associated with normal BMI, fewer tender joints, less pain, less fatigue, fewer pain regions, less disability, better HRQoL, and biologic treatment. In 2010, 628 patients reported NCP or CRP, whereas 114 of them reported CWP in 2017. Transition to CWP was associated with female gender, obesity, more tender and swollen joints, higher pain-related variables, worse disability, and worse HRQoL.Conclusion: There are modifiable factors associated with transitions from and to CWP that could be identified. Paying attention to these factors could improve pain treatment in the management of RA.

Sociodemographic determinants in the evolution of pain in inflammatory rheumatic diseases: results from ESPOIR and DESIR cohorts

Objective

To determine whether socio-demographic factors are associated with heterogeneity in pain evolution in inflammatory rheumatic diseases (IRDs) after accounting for disease-specific characteristics in a system with universal health care.

Methods

This analysis included the data from two prospective observational cohorts of early IRDs (ESPOIR for early RA and DESIR for early SpA). Data on pain was measured, respectively, on 13 and 9 occasions spanning 10 and 6 years of follow-up using the Short-Form 36 bodily pain score for 810 participants of ESPOIR, and 679 participants of DESIR. Linear mixed models were used to characterize differences in pain evolution as a function of age (tertiles), sex, ethnicity, education, marital, and professional status, after accounting for disease-related, treatment, lifestyle, and health factors.

Results

While transitioning from early (disease duration ≤6 months for RA and ≤3 years for SpA) to long-standing disease, differences in pain evolution emerged as a function of age (P < 0.001), sex (P = 0.050), and ethnicity (P = 0.001) in RA, and as a function of age (P = 0.048) in SpA; younger age, males, and Caucasians exhibited lower pain in the latter phases of both diseases. Highly educated participants (RA, β = −3.8, P = 0.007; SpA, β = −6.0, P < 0.001) for both diseases, and Caucasians (β = −5.6, P = 0.021) for SpA presented with low pain early in the disease, with no changes throughout disease course.

Conclusion

Being older, female, non-Caucasian and having lower education was found to be associated with worse pain in early and/or long-standing IRDs, despite universally accessible health-care. Early identification of at-risk populations and implementation of multidisciplinary strategies may reduce patient-reported health outcome disparities.

Trial registration registrations

ESPOIR: ClinicalTrials.gov, www.clinicaltrials.gov, NCT03666091. DESIR: ClinicalTrials.gov, www.clinicaltrials.gov, NCT01648907.

Spreading of Pain in Patients with Chronic Pain is Related to Pain Duration and Clinical Presentation and Weakly Associated with Outcomes of Interdisciplinary Pain Rehabilitation: A Cohort Study from the Swedish Quality Registry for Pain Rehabilitation (SQRP)

Introduction

The extent to which pain is distributed across the body (spreading of pain) differs largely among patients with chronic pain conditions and widespread pain has been linked to poor quality of life and work disability. A longer duration of pain is expected to be associated with more widespread pain, but studies are surprisingly scarce. Whether spreading of pain is associated with clinical presentation and treatment outcome in patients seen in interdisciplinary multimodal pain rehabilitation programs (IMMRPs) is unclear. The association between spreading of pain and (1) pain duration (2) clinical presentation (eg, pain intensity, pain-related cognitions, psychological distress, activity/participation aspects and quality of life) and (3) treatment outcome were examined.

Methods

Data from patients included in the Swedish Quality Registry for Pain Rehabilitation were used (n=39,916). A subset of patients that participated in IMMRPs (n=14,666) was used to examine whether spreading of pain at baseline predicted treatment outcome. Spreading of pain was registered using 36 predefined anatomical areas which were summarized and divided into four categories: 1–6 regions with pain (20.6% of patients), 7–12 regions (26.8%), 13–18 regions (22.0%) and 19–36 regions (30.6%).

Results

More widespread pain was associated with a longer pain duration and a more severe clinical picture at baseline with the strongest associations emerging in relation to health and pain aspects (pain intensity, pain interference and pain duration). Widespread pain was associated with a poorer overall treatment outcome following IMMRPs at both posttreatment and at a 12-month follow-up, but effect sizes were small.

Discussion

Spreading of pain is an indicator of the duration and severity of chronic pain and to a limited extent to outcomes of IMMRP. Longer pain duration in those with more widespread pain supports the concept of early intervention as clinically important and implies a need to develop and improve rehabilitation for patients with chronic widespread pain.

Chronic Pain and Assessment of Pain Sensitivity in Patients With Axial Spondyloarthritis: Results From the SPARTAKUS Cohort

OBJECTIVE

To study differences in pain reports between patients with ankylosing spondylitis (AS) and nonradiographic axial spondyloarthritis (nr-axSpA), and to assess how pain sensitivity measures associate with disease and health outcomes.

METHODS

Consecutive patients with axial SpA (axSpA) were enrolled in the population-based SPARTAKUS cohort (2015-2017) and classified as AS (n = 120) or nr-axSpA (n = 55). Pain was assessed with questionnaires (intensity/duration/distribution) and computerized cuff pressure algometry to measure pain sensitivity (pain threshold/pain tolerance/temporal summation of pain). Linear regression models were used to compare pain measures between patients with AS and nr-axSpA, and to assess associations between pain sensitivity measures and disease and health outcomes.

RESULTS

Of 175 patients with axSpA, 43% reported chronic widespread pain, with no significant differences in any questionnaire-derived or algometry-assessed pain measures between patients with AS and nr-axSpA. Lower pain tolerance was associated with longer symptom duration, worse Ankylosing Spondylitis Disease Activity Score using C-reactive protein (ASDAS-CRP), Bath Ankylosing Spondylitis Functional Index, and Bath Ankylosing Spondylitis Metrology Index (BASMI), more pain regions, unacceptable pain, worse Maastricht AS Enthesitis Score (MASES), fatigue, anxiety, and health-related quality of life. Further, lower pain threshold was associated with worse ASDAS-CRP and MASES, whereas higher temporal summation was associated with longer symptom duration, unacceptable pain, and worse BASMI.

CONCLUSION

Chronic pain is common in axSpA, with no observed differences in any pain measures between patients with AS and nr-axSpA. Further, higher pain sensitivity is associated with having worse disease and health outcomes. The results indicate that patients with AS and nr-axSpA, in line with most clinical characteristics, have a similar pain burden, and they highlight large unmet needs regarding individualized pain management, regardless of axSpA subgroup.

Women's experiences of the journey to chronic widespread pain: a qualitative study

BACKGROUND

Chronic widespread pain (CWP) is a musculoskeletal disorder that affects approximately 10% of the population. It is more common in women than in men. It is important to understand how CWP develops and how it is maintained in order to prevent poor pain prognosis. Long term studies have shown that a mere part improves over time or fluctuates in their CWP condition. Female gender is one of the factors associated with persistence of CWP, suggesting men and women may experience their journey to CWP differently. The aim of the study was to explore women's experiences of the journey to CWP.

METHODS

19 women between 45 and 67 years of age who had not reported CWP in the EPIPAIN survey in 1995, but reported CWP in 2016, participated in the study. Data was collected through individual interviews, where open-ended questions were used to explore the women's experiences of their pain journey. The interviews were analyzed with a manifest qualitative content analysis.

RESULTS

The women described their journey to CWP in terms of triggering, aggravating, and consolidating factors, from which three different categories emerged. Experiencing that environmental circumstances affect the pain journey refers to factors outside the women's immediate control, which appeared as unmanageable work-related demands, lack of social support, unfavorable physical environments, and traumatic events. Experiencing that lifestyle affects the pain journey refers to events that are consciously or unconsciously carried out by the women, including different levels of physical efforts and unfavorable behaviors. Experiencing that personal attributes affect the pain journey refers to the women's characteristics in terms of an anxious state of mind and adverse biological impact.

CONCLUSIONS

The women experienced that environmental circumstances, lifestyle, and personal attributes affected their CWP. How these adversities influenced the pain journey varied among the women. These findings show that women are conscious of the complexity of the condition and can describe the broad context of their pain journey. This study confirms the complexity of pain progress and highlights the individual's awareness of this complexity, which is important to consider when introducing interventions, and when expecting compliance to interventions.

Sex differences in disease activity and efficacy of treatment in spondyloarthritis: is body composition the cause?

PURPOSE OF REVIEW

The body composition and fat distribution is different between men and women, with different levels of circulating adipokines. These differences become more evident when suffering from an inflammatory disease, such as spondyloarthritris. In this review, we will explore the influence of obesity, body composition and adipokines on the differences in disease activity, progression and response to treatment, between men and women with spondyloarthritis.

RECENT FINDINGS

Obesity, mainly determined by the body fat content, which is higher in women, is related to worse disease activity scores. Men with higher disease activity lose more muscle mass than women. Leptin, which is usually found at higher levels in overweight women, seems to be associated with greater spinal radiographic progression when it rises during the course of the disease. Being a woman and obesity, mainly because of the body fat content, are related to a worse response to TNF-α blockers.

SUMMARY

Overlooking biological sex variation in body composition, circulating adipokines and hormonal levels, and the subsequent differences in clinical presentation, may ultimately hamper clinical treatment.