Evaluating the associations between dysautonomia, gastrointestinal transit, and clinical phenotype in patients with systemic sclerosis

OBJECTIVE

Our objective was to identify systemic sclerosis (SSc) patients with a high burden of autonomic symptoms and to determine whether they have a distinct clinical phenotype, gastrointestinal (GI) transit or extraintestinal features.

METHODS

In a prospective cohort of SSc patients with GI disease, clinical data were systematically obtained at routine visits. Dysautonomia was identified by the Composite Autonomic Symptom Score (COMPASS)-31questionnaire. GI transit was measured by whole-gut scintigraphy. Associations between total COMPASS-31 scores and clinical features, GI symptoms, and transit were evaluated. Comparisons between patients with global autonomic dysfunction [(GAD); ≥5 positive COMPASS-31 subdomains] and those with limited autonomic dysfunction [(LAD); <5 positive subdomains] were also studied.

RESULTS

91 patients with SSc and GI involvement were included [mean age 57, 90% female, 74% limited cutaneous disease, 83% significant GI disease (Medsger score ≥2)]. The mean COMPASS-31 score in SSc was higher than controls (38.8 vs. 7.2). 33% had GAD, 67% had LAD. Patients with GAD were more likely to have limited SSc (93% vs. 65%; p<0.01) and have sicca symptoms (100% vs. 77%; p=0.01). Gastric and colonic transit were faster in patients with GAD (p<0.05). Upper GI involvement (Medsger GI score of 1 or 2) was associated with higher total COMPASS-31 scores (p=0.02).

CONCLUSION

Symptoms of global dysautonomia are seen in up to one-third of patients with SSc and GI involvement. Identifying specific clinical characteristics associated with GAD in SSc will help to identify a population that may benefit from therapies that modulate the autonomic nervous system.

Diagnostic Yield of Computed Tomography for Cancer Detection in a Tertiary Referral Population of Idiopathic Inflammatory Myositis Patients

OBJECTIVE

To inform guidance for cancer detection in patients with idiopathic inflammatory myopathy (IIM), we evaluated the diagnostic yield of computed tomography (CT) imaging for cancer screening/surveillance within distinct IIM subtypes and myositis-specific autoantibody strata.

METHODS

We conducted a single-center, retrospective cohort study in IIM patients. Overall diagnostic yield (number of cancers diagnosed/number of tests performed), percentage of false positives (number of biopsies performed not leading to cancer diagnosis/number of tests performed), and test characteristics were determined on CT of the chest and abdomen/pelvis.

RESULTS

Within the first 3 years since IIM symptom onset, a total of 9 of 1,011 (0.9%) chest CT scans and 12 of 657 (1.8%) abdomen/pelvis CT scans detected cancer. Diagnostic yields for both CT of the chest and CT of the abdomen/pelvis were highest in dermatomyositis, specifically anti-transcription intermediary factor 1γ (2.9% and 2.4% for CT of the chest and abdomen/pelvis, respectively). The highest percentage of false positives was in patients with antisynthetase syndrome (ASyS) (4.4%) and immune-mediated necrotizing myopathy (4.4%) on CT of the chest, and ASyS (3.8%) on CT of the abdomen/pelvis. Patients ages <40 years old at IIM onset had both low diagnostic yields (0% and 0.5%) and high false-positive rates (1.9% and 4.4%) for CT of the chest and abdomen/pelvis, respectively.

CONCLUSION

In a tertiary referral cohort of IIM patients, CT imaging has a wide range of diagnostic yield and frequency of false positives for contemporaneous cancer. These findings suggest that cancer detection strategies targeted according to IIM subtype, autoantibody positivity, and age may maximize cancer detection while minimizing the harms and costs of over-screening.

The yin and yang of GSM and low sexual desire

Numerous surveys have documented that sexuality and/or sexual activity is important to women at all stages of adulthood, including postmenopause. Genitourinary syndrome of menopause (GSM) and hypoactive sexual desire disorder (HSDD) are common disorders in postmenopausal women and may co-occur. Both are often undiagnosed due to a lack of knowledge of the disorder, health-care professional discomfort in discussing sexual problems or a lack of routine screening. It is incumbent upon health-care professionals to identify and differentiate these conditions in women through a biopsychosocial assessment, and may require a focused physical examination. Numerous treatments, both non-pharmacologic and pharmacologic, are available to address GSM and HSDD.

Association of Anti-CCAR1 Autoantibodies With Decreased Cancer Risk Relative to the General Population in Patients With Anti-Transcriptional Intermediary Factor 1γ-Positive Dermatomyositis

OBJECTIVE

To describe the disease specificity, clinical phenotype, and risk of cancer in dermatomyositis (DM) patients with autoantibodies against cell division cycle and apoptosis regulator protein 1 (anti-CCAR1).

METHODS

The frequency of anti-CCAR1 autoantibodies was measured by enzyme-linked immunosorbent assay in the serum of DM patients from 2 independent cohorts (Johns Hopkins and Stanford), with patients with several other rheumatic diseases and healthy controls used as comparators. Clinical features and the risk of cancer incidence relative to that in the general population were determined in anti-CCAR1-positive DM patients.

RESULTS

Anti-CCAR1 antibodies were significantly associated with anti-transcriptional intermediary factor 1γ (anti-TIF1γ) antibodies present in the serum of patients with DM: 80 (32%) of 252 anti-TIF1γ-positive DM patients versus 14 (8%) of 186 anti-TIF1γ-negative DM patients were positive for anti-CCAR1 antibodies (P < 0.001). Anti-CCAR1 antibodies were not detected in any of the 32 serum samples from healthy controls, and were present at very low frequencies in the sera of patients with other rheumatic diseases: 1 (2.3%) of 44 patients with anti-hydroxymethylglutaryl-coenzyme A reductase-positive necrotizing myopathy, 1 (2.3%) of 44 patients with inclusion body myositis, and 3 (6.5%) of 46 patients with systemic lupus erythematosus were positive for anti-CCAR1 antibodies. Upon examining data on occurrence of cancer from the onset of DM onward, the observed number of cancers diagnosed in anti-TIF-1γ-positive DM patients was significantly greater than expected in both cohorts, with a standardized incidence ratio (SIR) of 3.49 (95% confidence interval [95% CI] 2.39-4.92) in the Johns Hopkins cohort and a SIR of 4.54 (95% CI 3.04-6.52) in the Stanford cohort (each P < 0.001). DM patients who were both anti-TIF1γ positive and anti-CCAR1 positive had lower SIRs for cancer, with a SIR of 1.78 (95% CI 0.77-3.51) (P = 0.172) in the Johns Hopkins cohort and a SIR of 1.61 (95% CI 0.44-4.13) (P = 0.48) in the Stanford cohort.

CONCLUSION

Anti-CCAR1 autoantibodies are specific for anti-TIF1γ-positive DM. Their presence in anti-TIF1γ-positive patients attenuates the risk of cancer to a level comparable to that seen in the general population.

Subsets of Idiopathic Inflammatory Myositis Enriched for Contemporaneous Cancer Relative to the General Population

OBJECTIVE

This study investigates cancer risk in idiopathic inflammatory myopathy (IIM) relative to the general population.

METHODS

We conducted a single-center, retrospective cohort study of IIM patients and malignancy. Myositis-specific and -associated autoantibodies were determined by Euroimmun line blot, enzyme-linked immunosorbent assay, and immunoprecipitation. We calculated standardized prevalence ratios (SPRs) and adjusted for calendar year, age, sex, race, and ethnicity by comparing observed cancers in IIM patients versus expected cancers in the general population using the Surveillance, Epidemiology, and End Results registry.

RESULTS

Of 1,172 IIM patients, 203 (17%) patients with a cancer history were studied. Over a median follow-up of 5.2 years, the observed number of IIM patients diagnosed with cancer was increased 1.43-fold (SPR 1.43 [95% confidence interval (95% CI) 1.15-1.77]; P = 0.002). Within 3 years of IIM symptom onset, an increased SPR was observed for anti-transcription intermediary factor 1γ (anti-TIF1γ)-positive patients for ovarian and breast cancer (ovarian SPR 18.39 [95% CI 5.01-47.08], P < 0.001; breast SPR 3.84 [95% CI 1.99-6.71], P < 0.001). As expected, anti-TIF1γ positivity was associated with a significantly elevated SPR; however, only 55% (36 of 66) of all cancers within 3 years of dermatomyositis onset were observed in anti-TIF1γ-positive patients. Other myositis-specific autoantibodies, including anti-Mi-2, anti-small ubiquitin-like modifier activating enzyme (SAE), and anti-nuclear matrix protein 2 (NXP-2), accounted for 26% (17 of 66) of cancers diagnosed within 3 years of dermatomyositis onset. No cancer association, positive or negative, was observed for patients with antisynthetase, anti-melanoma differentiation-associated protein 5 (anti-MDA-5), or anti-hydroxymethylglutaryl-coenzyme A reductase (anti-HMGCR) antibodies.

CONCLUSION

In a tertiary referral center population, anti-TIF1γ was most strongly associated with breast and ovarian cancer. Patients with antisynthetase, anti-MDA-5, or anti-HMGCR antibodies had the same cancer risk as the general population.

Clinical Subgroups and Factors Associated With Progression in Patients With Inclusion Body Myositis

BACKGROUND AND OBJECTIVES

Sporadic inclusion body myositis (IBM) is the most common acquired myopathy in individuals older than 50 years. The disorder is slowly progressive, and although many therapies have been investigated, response has generally been poor. Clinical heterogeneity may influence treatment responsiveness; however, data regarding heterogeneity in IBM are limited and often conflicting. We aim to identify clinically distinct subgroups within a large IBM cohort and prognostic factors for disease progression.

METHODS

Clinical, histologic, radiologic, and electrophysiologic data were analyzed for all patients with IBM and other forms of myositis enrolled in a longitudinal cohort from The Johns Hopkins Myositis Center from 2003 to 2018. Patients with IBM were included if they met at least one of the following criteria: Griggs possible, European Neuromuscular Centre 2011 probable, or Lloyd-Greenberg data-derived criteria for IBM. Univariate, multivariate, and graphical analyses were used to identify prognostic factors in patients with IBM. Thus, linear and logistic regressions were used to adjust for potential confounding variables. The evolution of creatine kinase and muscle strength was studied using multilevel linear regression models. Nonmodifiable risk factors (sex, race, disease duration, and age at the onset of first symptoms) were used as adjusting covariates for the regression analyses.

RESULTS

Among the 335 patients meeting the inclusion criteria for IBM, 64% were male with an average age of disease onset of 58.7 years and delay to diagnosis of 5.2 years. Initial misdiagnosis (52%) and immunosuppressant treatment (42%) were common. Less than half (43%) of muscle biopsies demonstrated all 3 pathologic hallmarks: endomysial inflammation, mononuclear cell invasion, and rimmed vacuoles. Black patients had significantly weaker arm abductors, hip flexors, and knee flexors compared with non-Black patients. Female patients had stronger finger flexors and knee extensors compared with their male counterparts. Younger age (<50 years) at onset was not associated with increased weakness.

DISCUSSION

Our study demonstrates that female and Black patients have distinct clinical phenotypes and trajectories within the overarching IBM clinical phenotype. These subgroups may have different responses to therapies, which may influence the design of future clinical trials in IBM.

Current status of clinical outcome measures in inclusion body myositis: a systematised review

OBJECTIVES

Sporadic inclusion body myositis (IBM) is a debilitating idiopathic inflammatory myopathy (IIM) which affects hand function, ambulation, and swallowing. There is no approved pharmacological therapy for IBM, and there is a lack of suitable outcome measure to assess the effect of an intervention. The IBM scientific interest group under IMACS reviewed the previously used outcome measures in IBM clinical studies to lay the path for developing a core set of outcome measures in IBM.

METHODS

In this systematised review, we have extracted all outcome measures reported in IBM clinical studies to determine what measures were being used and to assess the need for optimising outcome measures in IBM.

RESULTS

We found 13 observational studies, 17 open-label clinical trials, and 15 randomised control trials (RCTs) in IBM. Six-minute walk distance, IBM-functional rating scale (IBM-FRS), quantitative muscle testing, manual muscle testing, maximal voluntary isometric contraction testing, and thigh muscle volume measured by MRI were used as primary outcome measures. Twelve different outcome measures of motor function were used in IBM clinical trials. IBM-FRS was the most used measure of functionality. Swallowing function was reported as a secondary outcome measure in only 3 RCTs.

CONCLUSIONS

There are inconsistencies in using outcome measures in clinical studies in IBM. The core set measures developed by the IMACS group for other IIMs are not directly applicable to IBM. As a result, there is an unmet need for an IBM-specific core set of measures to facilitate the evaluation of new potential therapeutics for IBM.

Gastroparesis in systemic sclerosis: a detailed analysis using whole-gut scintigraphy

OBJECTIVES

Gastroparesis is a common complication of SSc. We sought to determine the degree of overlap between gastroparesis and dysmotility in other areas of the gut, correlate our findings with gastrointestinal (GI) symptoms, and examine associations between gastroparesis and SSc features.

METHODS

Whole-gut scintigraphy was performed on SSc patients who were enrolled in the Johns Hopkins Scleroderma Cohort, for whom detailed longitudinal clinical and serologic data are collected. A subset of patients completed the University of California Los Angeles Scleroderma Clinical Trial Consortium Gastrointestinal Tract Instrument 2.0 (UCLA GIT 2.0) to quantify their GI symptoms. We examined associations between the presence and severity of gastroparesis, GI symptoms, and SSc clinical features.

RESULTS

Ninety-seven SSc patients with and without GI symptoms underwent whole-gut scintigraphy and completed the gastric emptying study. Of the 97, 34 (35%) met criteria for gastroparesis. Of the measures assessed, delayed liquid emptying captured more patients with delayed gastric transit than delayed solid emptying (74% vs 55%), and percentage liquid emptying correlated best with GIT Reflux (ρ = -0.33, P = 0.01) and Distension (ρ = -0.30, P = 0.03) scores. Of 33 patients with gastroparesis, 30 (91%) had abnormal transit in other areas of the GI tract. Higher anti-centromere protein B (CENP-B) titres correlated with slower gastric emptying (ρ = -0.26, P = 0.03), but no specific clinical features of SSc were associated with gastroparesis.

CONCLUSIONS

Gastric emptying of liquids when given alongside solids may be more sensitive and provide a more clinically relevant measure of gastroparesis in SSc than solid gastric emptying or liquid gastric emptying alone. SSc patients with gastroparesis frequently have dysmotility in other areas of the GI tract, underscoring the need for whole-gut scintigraphy to evaluate the entire gut.

Mushroom supplements triggering a flare of HMGCR immune mediated necrotising myopathy

Hydroxyl-methyl-glutaryl-Co-A reductase (HMGCR) immune mediated necrotising myopathy (IMNM) is a rare autoimmune myositis that is thought to be triggered by statins and responds to immunomodulation. We report a case of a woman in her 30s with HMGCR IMNM without a history of statin exposure who had a clear flare of her myositis after beginning mushroom supplements. Mushrooms are natural HMGCR inhibitors, and this is the first case to demonstrate a flare triggered by mushrooms in a patient with known HMGCR IMNM. This case highlights the importance of reviewing diet and supplements in patients with IMNM. It also emphasises the importance of strict statin avoidance for patients with IMNM even when the myositis is under good control.

The Cancer Risk Profile of Systemic Lupus Erythematosus Patients

ABSTRACT

Systemic lupus erythematosus (SLE) patients have a well-established increased risk for cancer. Research from the past 2 decades has identified the specific malignancies that afflict SLE patients at disproportionate rates. Systemic lupus erythematosus patients are at heightened risk for several hematologic malignancies as well as for certain solid tumors, including lung, thyroid, and hepatobiliary cancers. They are at decreased risk for several cancers as well, including prostate and melanoma. Improved understanding of the unique cancer risk profile of SLE patients has led some professional societies to recommend specialized cancer screening and prevention measures for these patients and has enabled clinicians to better serve the SLE patient population.

The Effect of Mycophenolate Mofetil as First-Line Therapy on the Timing of Urine Protein-to-Creatinine Ratio Reduction in Immunosuppressant-Naive Patients With Lupus Nephritis at a Single Center

BACKGROUND/OBJECTIVES

Early response to immunosuppressive therapy predicts good renal outcome in lupus nephritis (LN). The purpose of this study was to assess the effect of mycophenolate mofetil (MMF) on the timing of urine protein-to-creatinine ratio reaching 200 mg or less after starting MMF as initial therapy for class III, IV, or V in immunosuppressant-naive patients with LN.

METHODS

Patients who had a diagnosis of biopsy-proven LN were included in this cohort study. The initial dose of MMF was 1000 mg twice daily. If no improvement, it was increased to 1500 mg twice daily after 1 month. For statistical analysis, exact binomial distribution 95% confidence intervals were calculated.

RESULTS

Nine patients were identified. There were 3 patients with class III, 3 with class IV, 1 with class III to V, 1 with class II to V, and 1 with class V lupus nephritis. The majority were African Americans (70%). At baseline, proteinuria ranged between 0.41 and 4 g, and 88% had normal estimated glomerular filtration rate. Forty-four percent of patients reached 0.28 g of proteinuria within 8 weeks of starting MMF (95% confidence interval, 14%-79%), all of which maintained the same level of response and normal estimated glomerular filtration rate at 12 months. Thirty-three percent of patients achieved the American College of Rheumatology complete response at 8 weeks.

CONCLUSIONS

This study demonstrates that only a minority of immunosuppressant-naive LN patients achieved the American College of Rheumatology complete response at 8 weeks after initiation of MMF. A rapid decline in the proteinuria to 0.28 g within the first 8 weeks of the treatment correlated strongly with achieving the same level of response at 12 months.

The phenotype of myositis patients with anti-Ku autoantibodies

OBJECTIVES

To define the clinical features of anti-Ku-positive myositis patients and to determine the reliability of the Euroline assay to detect anti-Ku autoantibodies.

METHODS

Serum samples were screened for anti-Ku autoantibodies by Euroline and positive samples were confirmed by ELISA. The prevalence and severity of clinical features at onset and during follow-up in patients with anti-Ku-positive myositis were compared to those with dermatomyositis, immune-mediated necrotizing myopathy (IMNM), the antisynthetase syndrome (AS), inclusion body myositis (IBM), anti-U1-RNP-positive myositis, and anti-PM/Scl-positive myositis.

RESULTS

72 (2.9%) of 2475 samples were anti-Ku positive by Euroline using the manufacturer's recommended cutoff of >15. Just 17 (23.6%) of these were confirmed by ELISA and considered anti-Ku-positive for the analysis. Comparators included 169 IMNM, 168 AS, 387 IBM, 20 anti-U1-RNP-positive, and 47 anti-PM/Scl-positive patients. Muscle weakness was a presenting feature in 38% of anti-Ku-positive patients; 81% developed weakness during follow-up. Anti-Ku-positive patients had increased distal weakness compared to the non-IBM comparators. Interstitial lung disease (ILD) was present in 19% of anti-Ku-positive patients at the first visit and eventually developed in 56% of them. Throughout the course of disease, Gottron's papules and/or heliotrope rashes were less common in anti-Ku-positive patients (19%) compared to those with dermatomyositis (94%) or anti-PM/Scl-positive myositis (89%). Anti-Ku-positive patients never developed calcinosis.

CONCLUSIONS

The phenotype of anti-Ku positive myositis is distinguished by distal weakness, frequent ILD, infrequent rash, and no calcinosis. When used according to the current manufacturer's instructions, the Euroline assay has a high false-positive rate for anti-Ku autoantibodies.

Simultaneous assessment of colon motility in children with functional constipation by cine-MRI and colonic manometry: a feasibility study

BACKGROUND

Colonic manometry is the current reference standard for assessing colonic neuromuscular function in children with intractable functional constipation (FC). Recently, cine magnetic resonance imaging (cine-MRI) has been proposed as a non-invasive alternative. We compared colonic motility patterns on cine-MRI with those obtained by manometry in children, by stimulating high-amplitude propagating contractions (HAPCs) with bisacodyl under manometric control while simultaneously acquiring cine-MRI.

METHODS

After Institutional Review Board approval, adolescents with FC scheduled to undergo colonic manometry were included. A water-perfused 8-lumen catheter was used for colonic manometry recordings. After an intraluminal bisacodyl infusion, cine-MRI sequences of the descending colon were acquired for about 30 min simultaneously with colonic manometry. Manometry recordings were analysed for HAPCs. MRI images were processed with spatiotemporal motility MRI techniques. The anonymised motility results of both techniques were visually compared for the identification of HAPCs in the descending colon.

RESULTS

Data regarding six patients (three males) were analysed (median age 14 years, range 12-17). After bisacodyl infusion, three patients showed a total of eleven HAPCs with colonic manometry. Corresponding cine-MRI recorded high colonic activity during two of these HAPCs, minimal activity during seven HAPCs, while two HAPCs were not recorded. In two of three patients with absent HAPCs on manometry, colonic activity was recorded with cine-MRI.

CONCLUSIONS

Simultaneous acquisition of colonic cine-MRI and manometry in children with FC is feasible. Their motility results did not completely overlap in the identification of HAPCs. Research is needed to unravel the role of cine-MRI in this setting.

MRI in idiopathic, stable, slipped capital femoral epiphysis: evaluation of contralateral pre-slip

PURPOSE

Early diagnosis and treatment of slipped capital femoral epiphysis (SCFE) is important to prevent slip progression and avoid complications. We sought to determine if MRI findings in patients with unilateral SCFE could indicate 'pre-slip' or predict future SCFE in the contralateral hip.

METHODS

A prospective study evaluated patients with unilateral SCFE over a two-year period. MRI of the asymptomatic hip was performed within the perioperative period. Patients were followed with radiographs until a contralateral slip occurred or until physeal closure. Demographics, clinical stability, severity, posterior slope angle (PSA), modified Oxford Bone Score (mOBS) and patency of the triradiate cartilage were recorded and statistical analysis performed.

RESULTS

In all, 33 of 54 patients with unilateral SCFE were enrolled into the study. In all, 29 (87.8%) had complete follow-up. Five of the enrolled patients (15.2%) developed a sequential slip requiring in situ pinning. Six of 33 (18.2%) patients had positive MRI findings: four of which proceeded to sequential SCFE and two which did not. One sequential slip had a negative MRI. PSA predicted 1/11 sequential slips (sensitivity 9.09%, specificity 81.4%, positive predictive value (PPV) 11.1%, negative predictive value (NPV) 77.8%) and mOBS predicted 5/11 sequential slips (sensitivity 45.5%, specificity 93%, PPV 62.5%, NPV 87%). An open triradiate cartilage was present in 8/11 patients with sequential slips (sensitivity 72.7%, specificity 81.4%, PPV 50%, NPV 92.1%).

CONCLUSION

MRI findings consistent with 'pre-slip' were present in 66.7% of patients who developed a sequential SCFE. Further study on the utility/sensitivity of MRI in predicting sequential SCFE is warranted.

LEVEL OF EVIDENCE

II, diagnostic.

Fevers in Adult Lupus Patients

Variability in systemic lupus erythematosus (SLE) disease manifestations is well recognized. Lupus disease activity can range from mild to severe. Fever is a common manifestation of SLE and occurs in 36%-86% of patients. In the Modified Systemic Lupus Erythematosus Disease Activity Index (M-SLEDAI), fever is taken into account as disease activity scoring. Assessment of lupus patients with fever is an important diagnostic challenge, since the initial clinical presentation of a patient with lupus is very similar to the acute febrile phase of an infection. The attribution of fever to SLE holds only after other causes are excluded.

Cell surface hydrophobicity of colistin-susceptible vs resistant Acinetobacter baumannii determined by contact angles: methodological considerations and implications

Contact angle analysis of cell surface hydrophobicity (CSH) describes the tendency of a water droplet to spread across a lawn of filtered bacterial cells. Colistin-induced disruption of the Gram-negative outer membrane necessitates hydrophobic contacts with lipopolysaccharide (LPS). We aimed to characterize the CSH of Acinetobacter baumannii using contact angles, to provide insight into the mechanism of colistin resistance. Contact angles were analysed for five paired colistin-susceptible and resistant Ac. baumannii strains. Drainage of the water droplet through bacterial layers was demonstrated to influence results. Consequently, measurements were performed 0·66s after droplet deposition. Colistin-resistant cells exhibited lower contact angles (38·8±2·8-46·8±1·3°) compared with their paired colistin-susceptible strains (40·7±3·0-48·0±1·4°; anova; P<0·05). Contact angles increased at stationary phase (50·3±2·9-61·5±2·5° and 47·4±2·0-50·8±3·2°, susceptible and resistant, respectively, anova; P<0·05) and in response to colistin 32mgl(-1) exposure (44·5±1·5-50·6±2·8° and 43·5±2·2-48·0±2·2°, susceptible and resistant, respectively; anova; P<0·05). Analysis of complemented strains constructed with an intact lpxA gene, or empty vector, highlighted the contribution of LPS to CSH. Compositional outer-membrane variations likely account for CSH differences between Ac. baumannii phenotypes, which influence the hydrophobic colistin-bacterium interaction. Important insight into the mechanism of colistin resistance has been provided. Greater consideration of contact angle methodology is necessary to ensure accurate analyses are performed.