Update of Exocrine Functional Diagnostics in Chronic Pancreatitis Camilla Nøjgaard1, Søren Schou Olesen2, Jens Brøndum Frøkjær3 and Asbjørn Mohr Drewes2

Clin Physiol Funct Imaging (2012) doi: 10.1111/cpf.12011

REVIEW ARTICLE

Update of exocrine functional diagnostics in chronic pancreatitis Camilla Nøjgaard1, Søren Schou Olesen2, Jens Brøndum Frøkjær3 and Asbjørn Mohr Drewes2

1Department of Internal Medicine, Amager Hospital, Copenhagen, 2Mech-Sense, Department of Gastroenterology & Hepatology, Aalborg University Hospital, and 3Mech-Sense, Department of Radiology, Aalborg University Hospital, Aalborg, Denmark

Summary

Correspondence Diagnostics of pancreatic insufﬁciency rely mainly on tests of pancreatic exocrine Camilla Nøjgaard, Department of Internal Medi- function based on either measurement of pancreatic secretion or the secondary cine, Amager Hospital, Copenhagen, Denmark effects resulting from lack of digestive enzymes or imaging modalities. These E-mail: [email protected] methods have been developing rapidly over the last decades, and the aims of this Accepted for publication review were to describe exocrine functional testing and imaging of the pancreas Received 15 June 2012; accepted 07 November 2012 in chronic pancreatitis..

Key words chronic pancreatitis; enzymes; exocrine insufﬁciency; functional testing; imaging

Introduction Functional procedures The pancreas is an organ with an exocrine and endocrine function. Anatomically, it lies in the retroperitoneum and is Duodenal intubation tests (invasive procedures) therefore difficult to biopsy, and imaging may also be cum- Lundh test meal (also named Borgstrom€ test) bersome. Chronic pancreatitis (CP) is a chronic inflammatory condition characterized by irreversible morphological changes In Scandinavian literature, Lundh test meal has often been con- in the pancreas. During time, the inflammation leads to sidered as the gold standard for the definition of exocrine pan- destruction of the endocrine and exocrine tissue and thereby creatic insufficiency. It was described by Borgstrom,€ Dahlqvist exocrine and endocrine insufficiency, development of fibrosis and Lundh in 1962 (Borgstrom€ et al., 1962), but currently, and eventual calcifications. The diagnosis is based on a combi- only centres with special interest in pancreatitis use the test as nation of clinical information, imaging procedures and func- standard procedure. The procedure takes 2–3 h. In the fasting tional testing but rarely on histology (Layer et al., 1994). The patient, a tube is placed in the third part of duodenum, and diagnosis is easy when calcifications have developed or if his- the position is confirmed radiologically. The patient consumes tology is available, but in the early stages, the diagnosis is a standard meal, and during the next 80 min, the duodenal often challenging. This partly relates to the slow progression juice is aspirated. Volume and pH are noted for each specimen, of the anatomical and functional changes of the organ, and and concentrations of bicarbonate, lipase and amylase are the fact that the anatomical changes are not necessarily con- determined. If the volume of the duodenal aspirate is too small, nected to functional impairment. The degree of ductal changes the patient is stimulated by intravenous cholecystokinin. After- probably plays a larger role than the parenchymal abnormali- wards, the aspirate is investigated for the concentration of duo- ties (Domınguez-Munoz~ et al., 1995). Hence, diagnostics rely denal amylase and lipase. The pancreatic insufficiency can be mainly on (i) tests of pancreatic exocrine function based on divided into mild, moderate or severe insufficiency depending either measurement of pancreatic secretion or the secondary on the concentrations of the enzymes. Lundh test meal is effects resulting from lack of digestive enzymes or (ii) imag- thought to be more sensitive to mild and moderate insuffi- ing modalities. These methods have been developing rapidly ciency than faecal fat excretion according to the relation over the last decades, and the aims of this review were to between lipase secretion and stool fat, as patients with CP will describe state of the art of exocrine functional testing and first develop elevated faecal fat excretion if the lipase secretion imaging of the pancreas in CP. is lower than 5–7% of normal (DiMagno et al., 1973). © 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine 1 2 Update of exocrine functional diagnostics in chronic pancreatitis, C. Nøjgaard et al.

et al., 1998; Hardt et al., 2002; Chowdhury & Forsmark, The secretin–pancreozymin test 2003). In a study by Loser€ et al. (1996), the secretin–caerulein In non-Scandinavian countries, this test is most often used as test was used as gold standard to categorize pancreatic exo- the gold standard for exocrine pancreatic testing, but primarily crine insufficiency. Faecal elastase-1 sensitivity was 63% for in centres specifically interested in pancreatitis (Lankisch, mild, 100% for moderate, 100% for severe and 93% for all 1993). As the Lundh test meal, it is thought to be more sensi- patients with exocrine pancreatic insufficiency, and specificity tive to mild and moderate insufficiency than faecal fat excre- was 93%. Furthermore, the individual day-to-day variations of tion. In the fasting patient, a double-lumen tube is passed into faecal elastase-1 concentrations were low (mean CV = 15%; the third part of duodenum, and the position is confirmed Loser€ et al., 1996). These numbers are comparable with many radiologically. The duodenal juice is aspirated for a 15-min of the invasive pancreatic function tests, and the faecal elas- baseline period and then for three consecutive 15-min periods tase-1 test is increasingly used as the first-line measure of pan- after infusion of secretin and pancreozymin–cholecystokinin creatic exocrine insufficiency. The great success of the faecal intravenously. The volume and pH are noted for each speci- elastase-1 test has mainly been attributed to its non-invasive men, and concentrations of bicarbonate, lipase, trypsin, and nature. Furthermore, it is relatively cheap, easy to handle for chymotrypsin are determined (Burton et al., 1960). the patient and laboratory staff, and it can be stored at room temperature for more than a week. A few limitations, however, need to be considered when using the faecal elastase-1 The endoscopic secretin stimulation test test: First, diarrhoea or steatorrhoea of non-pancreatic origin By using this method, it is possible to perform a functional may artificially lower faecal elastase-1 concentration due to di- test of the pancreas simultaneously with an upper endoscopy lutional effects (Fischer et al., 2001). Second, faecal elastase-1 of the patient. The fasting patient is given secretin intrave- cannot be used to assess the response to pancreatic supple- nously. Thirty minutes after administration of secretin, the ment therapy as faecal elastase-1 remains low in stool despite duodenoscope is passed into the stomach and all gastric fluid pancreatic supplements. Finally, the relatively low sensitivity present is aspirated and discarded. The tip of the duodeno- in mild pancreatic disease needs to be taken into consideration scope is then placed closely to the ampulla of Vater, and duo- and limits the use of faecal elastase-1 to identify patients with denal aspirate is drawn for maximum 10 min and then pH is early and mild CP. measured. The measurements are excluded if pH is below 6Á0. The collected fluid is measured and analysed for the concen- Faecal fat excretion tration of bicarbonate, lipase and elastase (Jensen & Larsen, 2008; Law et al., 2012). Compared with the Lundh test meal, The simplest measurement of pancreatic enzyme action is endoscopic secretin stimulation test can differentiate between measurement of faecal fat excretion. Prior to faecal fat analy- normal and reduced exocrine function with acceptable accu- sis, the patient has to discontinue use of enzyme substitution racy, yielding positive and negative predictive values of 88% and under optimal conditions keep a constant fat intake of À and 83%, respectively. It is suggested that a combination of 100 g day 1 for 5 days. Then stool samples are collected for the concentration of bicarbonate and lipase is best to charac- analysis. To minimize sample errors, collection of three stool terize the patient’s exocrine pancreatic function into normal, samples is usually employed. The collected stool is homoge- reduced or insufficient (Jensen & Larsen, 2008). This method nized and fat extracted by organic solvent. Finally, the content is, however, not used routinely. of free fatty acids is quantified (Van De Kamer et al., 1949). À À A faecal fat quantity of >7 g day 1 (1Á9 mmol day 1) is considered to be abnormal and compatible with a diagnosis of Non-invasive exocrine pancreatic function tests pancreatic exocrine insufficiency. Clinical overt steatorrhoea is À typically present at faecal fat quantities >15 g day 1 Faecal elastase-1 À (4 mmol day 1). In addition, the fat absorption coefficient Pancreatic elastase-1 is a pancreas-specific enzyme that is not can be calculated as a quantitative index of fat absorption. This degraded during intestinal passage. It is approximately sixfold is accomplished according to the formula (dietary fat enriched in faeces compared with duodenal juice and can be intake À stool fat/dietary fat intake) 9 100% (normal measured in stool using a sensitive enzyme-linked immuno- >92Á5%; Chowdhury & Forsmark, 2003). Maldigestion of fat sorbent assay (ELISA) with monoclonal antibodies (Sziegoleit only occurs after approximately 90% of pancreatic lipase et al., 1989). Several studies have evaluated faecal elastase-1 in secretory capacity is lost, and a variety of other gastrointestinal patients with CP of varying severity based on morphological diseases are accompanied by steatorrhoea (DiMagno et al., and/or pancreatic function tests. Excellent correlation has been 1973). Consequently, quantitative faecal fat analysis is neither found between the faecal elastase-1 level and duodenal juice sensitive nor specific for exocrine pancreatic function. Taken volume, lipase, amylase, trypsin and bicarbonate output as together with the relatively time-consuming procedure and well as morphological changes of the pancreas as determined uncomfort for the patient, faecal fat excretion should be no by endoscopic retrograde cholangiopancreatography (Lankisch longer used for routine clinical diagnosis of exocrine © 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine Update of exocrine functional diagnostics in chronic pancreatitis, C. Nøjgaard et al. 3

pancreatic insufficiency, although it may still be useful in with severity assessed using the Cambridge classification selected cases to test the effectiveness of pancreatic enzyme (Sarner & Cotton, 1984). However, failure of visualization of replacement therapy (Lankisch, 1993). the entire ductal system due to ductal blockage and the risk of acute pancreatitis are limitations. Nowadays, routine imaging modalities applied in the evalu- Breath tests ation of CP are as follows: Computed tomography with one Several variations of breath tests with labelled carbon atoms in or more contrast enhancement phases, magnetic resonance the fatty acid triglyceride have been developed to measure fat imaging (MRI) with or without magnetic resonance cholan- digestion by pancreatic lipase. Exhalation of labelled CO2 is giopancreatography (MRCP) and ultrasound with a transab- measured after the ingestion of labelled triglycerides, which dominal or endoscopic approach (Fig. 1). The main focus is are usually given together with a standard meal. Tests vary in typically to describe glandular atrophy and calcifications, duct terms of the substrate, the standard with which the results are pathology, pseudocysts and complications such as abscess for- compared and the use of radioactive or non-radioactive mate- mation and acute inflammation. For endoscopic ultrasound, a rial for labelling. Various modifications have been proposed to classification system based on both parenchymal and ductal improve the specificity of breath tests for pancreatic function. morphology has been proposed, that is, the Rosemont criteria One modification involves the introduction of a mixed triglyc- (Seicean, 2010). Finally, tumour formation often has to be eride that consists of one medium-chain fatty acid and two ruled out, where positron emission tomography (PET) and long-chain fatty acids (13C-mixed triglyceride breath). The PET-computed tomography have a central position (Serrano principle of the test is that the two stearyl groups have to be et al., 2010). Recently, more advanced methods have emerged, split off the glycerol by lipase before 13C-octanoyl monoglyc- which also gives important information on both pancreatic eride, a medium-chain fatty acid, can be absorbed. This is function and tissue characteristics. Table 1 summarizes the 13 then rapidly metabolized and CO2 exhaled (Vantrappen advantages and limitations of the methods. et al., 1989). The test was applied to patients with CP of vari- able severity and found to have excellent sensitivity (100%) Ultrasound and specificity (85%) in severe CP, but low sensitivity (46%) and specificity (69%) in mild CP (Loser€ et al., 1998). Breath Sonoelastography examines the elastic properties of tissues by tests are unable to differentiate between pancreatic steator- applying a slight compression to the tissue and comparing the rhoea and other forms of fat malabsorption. However, the test images obtained before and after this compression. The tissue can measure the efficacy of enzyme replacement therapy and hardness can be evaluated with endoscopic ultrasound-guided can be used to make a judgement on the overall maldigestion. elastography to assess the degree of parenchymal fibrosis in For this reason, they have primarily been used to test the CP (Janssen et al., 2007). Elastography is now also possible in effectiveness of pancreatic enzyme replacement therapy instead transabdominal ultrasound (Erchinger et al., 2011). The tech- of the more time-consuming and unpleasant stool fat collec- nical development has substantially improved the image reso- tion. In this context, the 13C-mixed triglyceride breath was lution of transabdominal ultrasound, and using power shown to be an accurate method to evaluate the effect of Doppler and contrast-enhanced ultrasound, more information enzyme therapy on fat absorption (Domınguez-Munoz~ et al., on the pancreatic tissue structure can be obtained (Erchinger

2007). The metabolism of triglycerides to CO2 depends not et al., 2011). However, these new ultrasound-based techniques only on hydrolysis by pancreatic enzymes, but also on intesti- have primarily been evaluated for the ability to detect cancers nal absorption, hepatic metabolism and ventilation where dis- and not the severity of CP. ease affection can interfere with the accuracy of these tests (Chowdhury & Forsmark, 2003). Also, in spite of the many Magnetic resonance imaging available reports pertaining to diverse variations of breath tests, no single test have been thoroughly validated in larger On contrast-enhanced MRI, the degree of parenchymal fibrosis patient materials and international standardization is lacking. can be assessed as decreased and delayed enhancement on Hence, the use of breath tests mainly relies on local expertise serial contrast-enhanced images (Balcı, 2011). In secretin- and preference. stimulated MRCP, both the ductal system changes (including side branches) are better visualized and the exocrine function Functional imaging procedures can be evaluated with assessment of duodenal filling, changes in pancreatic duct calibre, change in pancreatic anteroposterior The development in imaging techniques has dramatically diameter, as well as change in signal intensity ratio between improved the diagnosis and evaluation of CP. Some decades pancreas and spleen on T1-weighted and arterial–venous ago, the evaluation was limited to radiography depicting calci- enhancement ratios (Balci et al., 2010). The findings are com- fications in severe CP. The ductal morphology has traditionally parable with endoscopic pancreatic function testing in the been assessed with endoscopic retrograde cholangiopancrea- evaluation of CP. Quantitative assessment of the pancreatic tography, which is based on intraductal contrast enhancement exocrine reserve by dynamic secretin-stimulated MRCP with © 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine 4 Update of exocrine functional diagnostics in chronic pancreatitis, C. Nøjgaard et al.

(a) (b)

(c) (d) Figure 1 Magnetic resonance imaging in chronic pancreatitis: axial T2-weighted (a) and 3D cholangiopancreatography (b) images in a patient with dilated and irregular main pancreatic duct, abnormal side branches and a small pseudocyst (arrow). Diffusion-weighted image (c) and map of the apparent diffusion coefﬁcient (d) with a measuring region posi- tioned in the corpus for assessment of parenchymal ﬁbrosis.

Table 1 The most important imaging modalities for the diagnosis of key features in chronic pancreatitis.

Glandular Ductal Exocrine Tissue Cancer atrophy Calciﬁcations morphology function characteristics evaluation Biopsy Comment

ERCP – (+) ++ –– – –Can be combined with EUS CT (contrast enhanced) ++ ++ + – (+) ++ CT perfusion ++ ++ + – ++ ++ + PET/CT ++ ++ + – +++– Transabdominal US ++ + – + (+) ++ Endoscopic US ++ + – ++++ Contrast-enhanced US ++ + – ++ + ++ As supplement to routine US Sonoelastography ++ + – ++ + ++ As supplement to routine US MRI with MRCP ++ – + – (+) + – Secretin-stimulated MRCP ++ – ++ ++ (+) + – Can be combined with DWI Contrast-enhanced MRI ++ – + – ++ + – Combined with MRCP MR DWI ++ – +++(with ++ + – Combined with ssMRCP) MRCP

The usefulness of the respective imaging modality for ascertaining the key features is indicated as ++ (excellent), + (sufﬁcient), (+) (not fully suf- ﬁcient) and – (not possible). CT, computed tomography; MRI, magnetic resonance imaging; MRCP, magnetic resonance cholangiopancreatography; US, ultrasound; EUS, endoscopic ultrasound; ERCP, endoscopic retrograde cholangiopancreatography; PET, positron emission tomography; DWI, diffusion-weighted imaging.

calculation of the duodenal filling volume correlated with the causes diffusion restriction and results in lower apparent diffu- faecal elastase-1 values in CP patients, making it possible to sion coefficient (Akisik et al., 2009). Furthermore, after secre- discriminate impaired and preserved pancreatic exocrine func- tin stimulation, the diffusion coefficients have either delayed tion using secretin-stimulated MRCP (Manfredi et al., 2012). or lower peak values in patients with reduced exocrine func- Diffusion-weighted imaging assesses the random motion of tion (Akisik et al., 2009). This is particularly useful in patients the water protons and is an emerging technology that can comple- with early-stage CP. Finally, diffusion-weighted images are ment standard MRI to assess the parenchymal changes associated helpful in the distinction between simple pancreatic cyst, with CP (see Fig. 1). Presence of parenchymal fibrosis in CP inflammatory cysts and cystic neoplasms (Balci et al., 2009). © 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine Update of exocrine functional diagnostics in chronic pancreatitis, C. Nøjgaard et al. 5

with severe morphological changes, faecal elastase-1 and Computed tomography breath test are often sufﬁcient screening procedures. In New multi-detector scanner generations with up to 256 slices patients with mild or moderate CP, the invasive tests are more allow computed tomography perfusion studies of the entire sensitive and should be considered. Some of the imaging pro- pancreas (and liver) assessing the parenchymal contrast cedures have the advantage that they combine a description enhancement with high temporal resolution. The pancreas can of the macro-and microstructural morphology with functional be evaluated with assessment of perfusion, peak enhancement changes, and this may improve early diagnosis and optimal intensity, time-to-peak and blood volume, and these parame- treatment. ters were changed in CP patients with exocrine insufﬁciency (Arikawa et al., 2012). Acknowledgment

Conclusions and guidelines for the future None.

The optimal functional testing of the exocrine pancreatic Conflict of interest statement function in CP should be non-invasive, safe, fast, cost-effec- tive and with a high sensitivity and specificity. In patients The authors have no conflict of interests.

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