Latent Crohn’s Disease Uncovered During Treatment with Secukinumab in a Patient with Ankylosing Spondilitis
Magdas Tudor-Mihai, Moșteanu Elena Ofelia*, Lebovici Andrei and Pop Teodora Atena
1Iuliu Hațieganu” University of Medicine and Pharmacy Cluj-Napoca, Romania
2Regional Institute of Gastroenterology and Hepatology “Prof.Dr. Octavian Fodor”, Cluj-Napoca, Romania
Received Date: 13/12/2020; Published Date: 23/12/2020
*Corresponding author: Ofelia Mosteanu, Iuliu Hațieganu, University of Medicine and Pharmacy Cluj-Napoca, Romania, Regional Institute of Gastroenterology and Hepatology “Prof.Dr. Octavian Fodor”, Cluj-Napoca, Romania
Cite this article: Magdas Tudor-Mihai, Moșteanu Elena Ofelia*, Lebovici Andrei and Pop Teodora Atena. Latent Crohn’s Disease Uncovered During Treatment with Secukinumab in a Patient with Ankylosing Spondilitis. Op Acc J Bio Sci & Res 6(5)-2020.
Salinity is a main factor of abiotic stresses to reduced crop production throughout the world. Current study investigates the effect of potassium chloride on biochemical parameter of two rice varieties; Basmati 385 (B-385) and SB (SB) grown under different concentration of sodium chloride (0, 50, 100, and 150mM). Salinity has negatively effect on biochemical characteristics of rice. In addition, photosynthetic pigment (Chl a, Chl b and carotenoids) lowered at different concentration of salt NaCl but significant increase was occurred at increasing concentration of KCl upto 100mM in both varieties. In addition, too, Proline accumulation increased as salinity increased but decreased as the concentration of KCl increased upto 100mM in both varieties. Salinity increased sodium ion concentration followed by decreased in Ca+2 and K+ as in KCl concentration the sodium ions decreased in shoot and root of both varieties. Furthermore, a possible decrease was observed in nitrogen and protein by increasing salinity level as compared to control. Unlikely, protein and nitrogen were increased with KCl concentration. Similarly, micro element (Cu, Fe and Mn) in roots and shoots of both varieties were decreased as level of NaCl increased though increased as the concentration of KCl increased upto 100mM. While zinc concentration increased as concentration of NaCl increased but decreased as KCl concentrations increased. The cadmium, lead and nickle were reduced as salinity increased but increased at 100mM of KCl.
Keywords: A biotic; Potassium Chloride; Sodium Chloride; Salinity; Stresses
Rice (Oryza sativa L.) is among the main staple food crop being used worldwide including Asian countries. Among abiotic stresses, salinity is one of the main factors in Asia, particularly in Pakistan that decline both productivity and quality of rice [1,2]. Soil Salinity is a major problem that effect crop productivity in both dry and semi-dry area. There are various types of salts in soils that turn down the productivity of crops, but among them NaCl is the most important one because it’s involved in disruption of plants and form unnecessary complex with other ions present in soil or plant . The osmotic effect, ionic toxicity and ionic imbalance in plant is due to the effect of salt [4,5]. The prevention of plant from the absorption of toxic ions i.e. Na+ and Cl- occur by certain mechanism- together with salt elimination and salt diffusion from leaves to roots [6,7]. It has been predictable that more than half of the yield possible of major crops is generally lost due to unfavorable growth circumstance such as drought or high salinity .
Potassium is one of important macronutrient, which playing a vital role in growth and development of plant in the whole life cycle . Potassium is a major component of protein synthesis, enzyme activation, the pH gradient, phloem uploading, turgor pressure regulation, stomatal functioning and the photosynthetic system , as well as controlling osmotic pressure and ionic balance during the disclosure of plants to salinity conditions . Exogenous potassium applications, such as potassium chloride (KCl), monopotassium phosphate (KH2PO4), potassium nitrate (KNO3), as well as potassium sulfate (K2SO4) which act as a fertilizers, are well-known for aiding nutrient uptake, water use efficiency, photosynthesis and growth performance in order to reduce salt stress [10-12]. The application of exogenous potassium fertilizers, which alleviates salt damage by enhancing K+ uptake and reducing Na+ uptake, leading to a decrease in the sodium Na+/K+ ratio, has been studies in many crop plants, i.e. pepper , sunflowers , ryegrass , cucumbers , strawberries  as well as rice .
Materials and Methods
1.1. Rice Seed collection and Processing
Rice seeds (Oryza sativa L.) of two varieties B-385 and SB were collected from National Agricultural Research Center (NARC) Islamabad, Pakistan. Seeds were surface sterilized through sodium hypochlorite (NaOCl) (3.5% (v/v)) for 3 or 4 minutes. Then seeds were rinsed through distilled water.
1.2. Hydroponic Cultring
After ten days of germination in controlled condition, the seedling was transferred to plastic pots containing 3 Liters of Hoagland solutions in green house . After 30 days harvested plant sample were oven dry for biochemical analysis such as Elemental analysis (Na+, K+, and Ca++) were analyzed by flame photometer by following  method using100ppm standard solution of Na, K, Ca. Micro element (Cu, Fe, Zn, Mn) and heavy metal (Ni, Cd, Pb) were determined by atomic adsorption spectrophotometer (Perkin ELMER, 2380) with air acetylene flame via hollow cathode lamps against the standard. Photosynthetic pigment determination occurs by  method. Determined of Proline occur by  method with a minor amendment. Total nitrogen and protein content determination occur through micro-Kjeldahl techniques by following  method with little bit modifications.
1.3. Data analysis
Statistical analyses of data occur by using Ms- Excel (statistic 9.1 versions) Statistic software. Each experiment has a replicate and its means value were compare with SD.
Potassium Chloride (KCl) modulate biochemical characteristics in Salt (NaCl) Stressed Rice (Oryza sativa) Varieties.
2.1. Encricment of Photosynethic Pigments
The Chlorophylls and carotenoid contents of both varieties: B-385 and SB showed negative correlation with increasing NaCl concentration. In contrast with increasing NaCl+KCl concentration it showed positive correlation up to certain limit. In addition, the chlorophyll a, b and carotenoid contents at 100mM of NaCl declined by 0.76 mg g-1, 0.39 mg g-1 and 12.40 mg g-1, respectively, over the control. At control, the overall performance of both varieties was good and chlorophyll a, b and carotenoid contents were 0.98 mg g-1, 0.62 mg g-1 and 19.20 mg g-1, respectively, which reduced to 0.76 mg g-1, 0.39 mg g-1 and 12.40 mg g-1 at 100mM of NaCl. In addition, too, the chlorophyll a, b and carotenoid contents at 100mM of NaCl+KCl in B-385 was enhanced i.e. 0.83 mg g-1, 0.50 mg g-1 and 14.60 mg g-1, correspondingly. Similarly, in case of SB the chlorophyll a, b and carotenoid contents at 100mM of NaCl declined by 00.25mg/g, 0.43mg/g and 44.30mg/g, respectively, over the control. However, increased to 0.40mg/g, 0.31mg/g and 58.02mg/g at 100mM of NaCl+KCl as shown in Table 1.
2.2. Potatium Cholride modulate Proline-amino acid and Total Protein contents in Rice
The amino acid proline accumulation in two varieties of rice; B-385 and SB were markedly increased as NaCl concentration increased, over the control, but the mutual effect of both NaCl+KCl decrease amino acid proline accumulation up to certain extant. The results showed that level of proline amount (0.098 mg g-1) elevated in response to 100mM of NaCl, over the control (0.042mg g-1). However, reduction was observed for B-385 in proline concentration (0.075mg g-1) at 100mM of NaCl+KCl. Similarly, in case of SB proline concentration (0.077mg g-1) is enhanced at 100mM of NaCl, over the control (0.0303mg g-1) but reduced to 0.068mg/g at 100mM of NaCl+KCl. Therefore, increase of proline amount treated with stress could be attributed to enhance proline amount, but potassium reduced sodium stress mention as Table 2.
In shoot and root of both varieties; B-385 and SB, nitrogen and protein contents were decreased as the NaCl concentration increased, while increased as concentration of NaCl+KCl increasing upto 100mM. The results showed that a possible reduction was observed in shoot of B-385 and (0.0030g and 0.0200g) at 100mM of NaCl concentration, over control (0.0037g and 0.0313g) as increased to 0.0036g and 0.0261g at 100mM of NaCl+KCl. Likewise shoots, a possible reduction was observed in roots (0.0057g and 0.0344 g) at 100mM of NaCl concentration, over control (0.0076g and 0.0452g) whereas increased to 0.0054g and 0.0322g at 100mM of NaCl+KCl.
Data regarding SB shoots showed that plants treated with 100mM of NaCl concentration recorded minimum nitrogen and protein content (0.0069g and 0.0411g) as compared to control (.0077g and 0.0467g) whilst increased to 0.0106g and 0.0458g at 100mM of NaCl+KCl. Likewise shoots, roots of plants treated with 100mM of NaCl concentration recorded minimum nitrogen and protein content (0.0096g and 0.0575g) as compared to control (0.0128g and0.0763g) whilst increased to 0.0107g and 0.0638g at 100mM of NaCl+KCl shown as Table 2.
2.3. Antagonistic profiling of Cellular Electrolytes (Na+, K+ and Ca2+) during Salt stress
Significant variations were notified in electrolytes (Na+, K+ and Ca2+) content in two varieties of rice i.e. B-385 and SB at different concentrations of NaCl. In present study, Na+ significantly increased and K+ and Ca2+ decrease with increasing NaCl in saline medium. While k+ and Ca2+ increased and a decline was observed for Na+ content with increasing NaCl+KCl. In shoot maximum K+, Ca2+ and Na+ contents were recorded for control (118 ppm, 66.66 ppm, and 57.33 ppm) as minimum were observed for 100 mM of NaCl concentration (92.83ppm, 56ppm and 82.33ppm), respectively. As at 100mM of NaCl+KCl values were 135ppm, 59.33ppm and 64ppm for Basmati-385. Data regarding roots of B-385 showed that highest values were recorded for control (49.33ppm, 62ppm and 27.66ppm) as lowest were observed for 100mM of NaCl concentration (41.66ppm, 52ppm and 50.66ppm). At 100mM of NaCl+KCl were 57.66ppm, 57ppm and 51ppm, respectively in Figure 1.
In shoot of SB K+, Ca2+ and Na+ contents at control were (86.66ppm, 65ppm and 34ppm) as at 100mM of NaCl concentration were (73.33ppm, 57ppm and 44.66ppm). But at 100mM of NaCl+KCl observed values were (57.66ppm 45.33ppm and 62ppm). While in roots K+, Ca2+ and Na+ contents at control were 60.66ppm, 64.66ppm and 33.66ppm, while at 100mM of NaCl concentration 44.33ppm, 56.66ppm and 65.33ppm, But at 100mM of NaCl+KCl 60.33ppm, 60ppm and 44.66ppm Figure 2.
2.4. Mudulation of Macro and Micro Elements
In Shoot and root of both varieties of rice; B-385 and SB Zinc concentration showed positive correlation with increasing NaCl concentration. But showed negative correlation with increasing of NaCl+KCl upto 100mM. In shoot and root of B-385 at control the zinc concentration was 1.57ppm, and 3.49ppm which elevated to 3.13ppm and 5.27ppm at 100mM of NaCl, but reduced to 2.17ppm and 4.08ppm at 100mM of NaCl+KCl. In shoot and roots of SB at control zinc concentration was 0.171ppm and 2.64ppm which enhanced to 1.32ppm and 3.49ppm at 100mM of NaCl, but reduced to 1.11ppm and 3.10ppm at 100mM of NaCl+KCl.
In shoot of B-385 at control the Copper, Iron and Manganese concentration was 0.098ppm,1.67ppm and 2.22ppm which reduced to 0.07ppm, 1.06ppm and 1.106ppm at 100mM of NaCl, but enhance to 0.91ppm, 1.15ppm and 1.85ppm at 100mM of NaCl+KCl. While in root at control the Copper, Iron and Manganese concentration was 0.21ppm, 1.26ppm and 1.90ppm which reduced to 0.11ppm, 0.73ppm and 1.02ppm at 100mM of NaCl, but increased to 0.26ppm, 1.15ppm and 1.35ppm at 100mM of NaCl+KCl.
In Shoot of SB at control Copper, Iron and Manganese concentration was 0.17ppm, 2.25ppm and 2.20ppm which reduced to 0.12ppm, 1.02ppm and 1.20ppm at 100mM of NaCl, but increased to 0.18ppm, 1.26ppm and 2.53ppm at 100mM of NaCl+KCl. While in root at control Copper, Iron and Manganese concentration was 0.31ppm, 2.27ppm and 1.13ppm which reduced to 0.16ppm, 1.42ppm and 0.48ppm at 100mM of NaCl, but increased to 0.25ppm, 1.47ppm and 1.55ppm at 100mM of NaCl+KCl.
Cadmium, Lead and Nickle concentration in shoot and root of both varieties; B-385 and SB were significantly reduced by increasing NaCl concentration and show negative correlation with sodium chloride. While in case of NaCl+KCl concentration cadmium, lead and nickle concentration increased Figures 3 & 4. In shoot of B-385, at control the cadmium, lead and Nickle concentration were 0.23ppm, 0.70ppm and 0.716ppm which reduced to 0.018ppm, 0.44ppm and 0.484ppm at 100mM of NaCl, but 0.035ppm, 0.513ppm and 0.665ppm at 100mM of NaCl+KCl. While in case of root at control the cadmium, lead and Nickle concentration were 0.09ppm, 0.83ppm and 2.7ppm which reduced to 0.034ppm, 0.06ppm and 1.20ppm at 100mM of NaCl, but 0.028ppm, 0.068ppm and 1.320ppm at 100mM of NaCl+KCl.
In shoot of SB cadmium, lead and Nicle concentration were 0.054ppm, 1.30ppm and 1.39ppm at control and 0.021ppm, 0.78ppm and 0.739ppm at 100mM of NaCl, but 0.048ppm, 0.91ppm and 0.784ppm at 100mM of NaCl+KCl. While in case of root cadmium, lead and Nickle concentration were 0.053ppm, 0.034ppm and 1.953ppm at control and 0.031ppm, 0.35ppm and 0.846ppm at 100mM of NaCl, but 0.043ppm, 0.37ppm and 0.85ppm at 100mM of NaCl+KCl.
Table 1: Coorelation of KCl and NaCl on photosynthetic pigment of rice varieties under Salinity (NaCl) condition.
Table 2: Combined effect of NaCl and KCl on Proline, Protein and Nitrogen contents of rice varieties under salt (NaCl) stress.
Figure 1: Effect of NaCl+KCl on Calcium, Sodiun and Potassium ions in shoots (A) and roots (B) of B-385 under various concentration of NaCl.
Figure 2: Effect of NaCl+KCl on Calcium, Sodium and Potassium ions in shoots (A) and roots (B) of SB under various concentration of NaCl.
Figure 3: Effect of NaCl+KCL on Copper, Zinc, Iron, manganese, Nickel, Lead, and Cadmium ions in a shoot (A) and root (B) of B-385 under various concentration of NaCl.
Figure 4: Effect of NaCl+KCL on Copper, Zinc, Iron, manganese, Nickel, Lead, and Cadmium ions in a shoot (A) and root (B) of SB under various concentration of NaCl.
It is widely known that there is a close association between IBD and SpA in terms of genetics, microbiota and immunology discorders [3,4]. In the etiopatogenesis of IBD, CD4 Th cells play a major role by starting and maintaining the autoimmune inflammation of the gastrointestinal tract, by producing pro-inflammatory cytokines. Beside CD4 Th cells, another subset of Th cells, Th17 cells, are overexpressed at this level and are positively regulated by IL-23, another proinflammatory cytokine produced by antigen-presenting cells, after the contact with the compounds of the pathological microbiota . The activation of IL-17/IL-23 axis is fundamentally connected to the etiology of both CD and AS, IL-17 being found extensively in the blood, the synovial fluid in AS and in the intestinal lamina propria of CD patients [7,8].
Human interleukin IL-17 was found to be involved in different autoimmune diseases, such as systemic sclerosis, multiple sclerosis, systemic lupus erythematosus, psoriasis, asthma, SpAs and IBD [9-14]. While IL-17 is a pro-inflammatory cytokine, current data suggests a protective role on the gastrointestinal tract in IBD patients . The importance of this paradox is to be seen in patients that benefit of biological treatment with IL-17 inhibitors and might associate a latent IBD.
Studies conducted with the objective of administering Secukinumab on CD animal models studies (2 ref trial) and on one human trial, which had to be completed prematurely because of the diseases’ unfavorable evolution compared to placebo, enforcing so the theory of IL-17 as being, in an unknown manner, a protective factor in the natural inflammatory evolution of CD. It is suggested that this difference may be due to the pathological microbiota found in IBD [16-18]. Using the data of these trials and knowing the statistical association between CD and SpA, the IL-17 molecule being overexpressed and playing different roles in both diseases, it might come handy that by inhibiting the IL-17/IL-23 path in SpA, the inflammation of the gut might worsen.
In Secukinumab’s summary of product characteristics, IBDs are mentioned in the section of special warnings and precautions for use, warning that the patients should be closely monitored. The latest retrospective analysis of pooled data from 21 clinical trials, containing 7355 patients, concluded that the cases of IBD during treatment with Secukinumab were uncommon . The reported incidence of CD among 794 patients treated for SpA was 0,1 per 100 patients/year, with 5 new onset cases of CD (0,63%) and an exacerbation found in 3 out of 5 patients with a history of CD. The question this case raised was whether our patient was having a silent CD that was activated by this treatment or he developed the disease on a normal gastrointestinal tract. Anamnestically, the patient did associate in time the onset of gastrointestinal manifestations with the use of Secukinumab.
Diarrhea is a common side effect of this treatment and the patients should be informed of the possibility of having an inactive IBD that might activate during this treatment and they should be advised to adress a specialist if the gastrointestinal symptoms persist. IL-17 positive cells are not detected in the mucosa of healthy individuals, infectious colitis or ischaemic colitis patients, but IL-17 levels are significantly elevated in active and even in inactive CD . Therefore, we can’t state that a subclinical CD was not present, taking into consideration also the frequency of IBD and SpA associating. Using the patient’s history and the current data available in the literature, we strongly believe that Secukinumab was the trigger of CD in this case.
Currently there are treatment guidelines just for IBD and SpA individually, but not any for both IBD and SpA, which would be needed in the near future, as more specific biological therapies emerge, targeting different inflammatory pathways. As written in the summary of product characteristics of Secukinumab, a close follow-up for IBD patients is needed, but, even if the new onset of CD is reported to have a low incidence, a gastroenterological monitoring would be recommended even for healthy individuals, because of the reported prevalence of IBD and SpA association.
A gastroenterological consult before the initiation of the treatment would be beneficial, since SpA may precede the onset of IBD [21,22] or may associate with an underlying asymptomatic intestinal inflammation . This case report is also enforcing the current data of IL-17 having a protective role in IBD, it’s path inhibition leading to exacerbation or to activation of a silent IBD. Of biological therapies, there are safer treatment schemes for a patient with AS and symptomatic or silent CD, which could include Ustekinumab, a human monoclonal antibody that is targeting the IL-12/IL-23 path, Infliximab, a chimeric monoclonal antibody that inhibits tumor necrosis factor alpha (TNFα) or Adalimumab, the first human monoclonal antibody that bind and neutralizez TNFα. The statistics and this case report are underlining the importance of a multi-disciplinary approach when prescribing biological therapy, including rheumatologists and gastroenterologists. Why the IL-17/IL-23 axis is having a „paradoxal” role on the gastrointestinal tract it still a question that’s laking an answer and represents a future research direction.
The authors are grateful to dr. Dana Alina Magdas for the careful reading of our manuscript and for the suggestions related to its improvement.
- Kostic AD, Xavier RJ, Gevers D (2014) The microbiome in inflammatory bowel disease: current status and the future ahead. Gastroenterology 146(6): 1489-1499.
- Ng SC, Shi HY, Hamidi N, Underwood FE, Tang W, Benchimol EI, et al. (2017) Worldwide incidence and prevalence of inflammatory bowel disease in the 21st century: a systematic review of population-based studies [Internet]. The Lancet. Elsevier.
- Salvarani C, Fries W (2009) Clinical features and epidemiology of spondyloarthritides associated with inflammatory bowel disease. World J Gastroenterol 15: 2449-2455.
- Shivashankar R, Loftus EV , Tremaine WJ, Bongartz T, Hamsen SW, et al. (2012) Incidence of spondyloarthropathy in patients with Crohn’s disease: a population-based study. J Rheumatol 39: 2148-2152.
- Ebringer A, Rashid T, Tiwana H, Wilson C (2007) A possible link between Crohn's disease and ankylosing spondylitis via Klebsiella infections. Clinical Rheumatology 26(3): 289-297.
- Menon B , Gullick NJ, Walter GJ (2014) Interleukin-17+CD8+ T cells are enriched in the joints of patients with psoriatic arthritis and correlate with disease activity and joint damage progression. Arthritis Rheumatol 66: 1272-1281.
- Veera, Klemetti, Paula, Sipponen, Mia, Kociubinski (2008) IL-23/IL-17 immunity as a hallmark of Crohn's disease [Internet]. OUP Academic. Oxford University Press.
- Kobayashi T, Okamoto S, Hisamatsu T, Kamada N, Chinen H, Saito R, et al. (2008) IL23 differentially regulates the Th1/Th17 balance in ulcerative colitis and Crohn's disease [Internet]. Gut. U.S. National Library of Medicine 57(12): 1682-1689.
- Chabaud M, Lubberts E, Joosten L (2001) IL-17 derived from juxta-articular bone and synovium contributes to joint degradation in rheumatoid arthritis. Arthritis Res 3: 168-177.
- Matusevicius D, Kivisakk P, He B (1999) Interleukin-17 mRNA expression in blood and CSF mononuclear cells is augmented in multiple sclerosis. Mult Scler 5:101-104.
- Kurasawa K, Hirose K, Sano H (2000) Increased interleukin-17 production in patients with systemic sclerosis. Arthritis Rheum 43: 2455-2463.
- Wong CK, Ho CY, Li EK (2000) Elevation of proinflammatory cytokine (IL-18, IL-17, IL-12) and Th2 cytokine (IL-4) concentrations in patients with systemic lupus erythematosus. Lupus 9: 589-593.
- Linden A (2001) Role of interleukin-17 and the neutrophil in asthma. Int Arch Allergy Immunol 126:179-184.
- Albanesi C, Scarponi C, Cavani A (2000) Interleukin-17 is produced by both Th1 and Th2 lymphocytes, and modulates interferon-γ- and interleukin-4-induced activation of human keratinocytes. J Invest Dermatol 115: 81-87.
- Sarra M, Pallone F, Macdonald TT, Monteleone G (2010) IL-23/IL-17 axis in IBD [Internet]. Inflammatory bowel diseases. U.S. National Library of Medicine 16(10): 1808-1813.
- Yen D, Cheung J, Scheerens H, Poulet F, McClanahan T, et al. (2006) IL-23 is essential for T cell-mediated colitis and promotes inflammation via IL-17 and IL-6 [Internet]. The Journal of clinical investigation. American Society for Clinical Investigation.
- Elson CO, Cong Y, Weaver CT, Schoeb TR, McClanahan TK, et al. (2007) Monoclonal anti-interleukin 23 reverses active colitis in a T cell-mediated model in mice [Internet]. Gastroenterology. U.S. National Library of Medicine 132(7): 2359-2370.
- Hueber W, Sands BE, Lewitzky S, Vandemeulebroecke M, Reinisch W, et al. (2012) Secukinumab, a human anti-IL-17A monoclonal antibody, for moderate to severe Crohn's disease: unexpected results of a randomised, double-blind placebo-controlled trial [Internet]. Gut. U.S. National Library of Medicine.
- Schreiber S, Colombel J-F, Feagan BG, Reich K, Deodhar AA, et al. (2019) Incidence rates of inflammatory bowel disease in patients with psoriasis, psoriatic arthritis and ankylosing spondylitis treated with secukinumab: a retrospective analysis of pooled data from 21 clinical trials [Internet]. Annals of the rheumatic diseases. BMJ Publishing Group.
- Fujino S, Andoh A, Bamba S, Ogawa A, Hata K, Araki Y, et al (2003) Increased expression of interleukin 17 in inflammatory bowel disease [Internet]. Gut. Copyright 2003 by Gut.
- Salvarani C, Vlachonikolis IG, van der Heijde DM, Fornaciari G, Macchioni P, et al. (2001) Musculoskeletal manifestations in a population-based cohort of inflammatory bowel disease patients [Internet]. Scandinavian journal of gastroenterology. U.S. National Library of Medicine.
- Orchard TR, Wordsworth BP, Jewell DP (1998) Peripheral arthropathies in inflammatory bowel disease: their articular distribution and natural history [Internet]. Gut. U.S. National Library of Medicine.
- Smale S, Natt RS, Orchard TR, Russell AS, Bjarnason I (2001) Inflammatory bowel disease and spondylarthropathy [Internet]. Wiley Online Library. John Wiley & Sons, Ltd.