Distal renal tubular acidosis in primary Sjögren syndrome

The association between dRTA and pSS has been described in various case
reports. It is unclear what the true prevalence of dRTA in pSS is. A study
which used the two available urinary acidification tests, the ammonium chloride
test and the furosemide/fludrocortisone test, to analyze the prevalence of dRTA
in a large group of pSS patients is lacking. Furthermore, the prevalence of
complications of dRTA is unclear. As described above, dRTA can lead to a low
bone mineral densitiy and kidney stones, which are serious complications.

Assessment of the exact prevalence of dRTA and its complications is important
because there is an effective treatment for both the symptoms and complications
of dRTA. Additionally, this study provides us the possibility to calculate the
sensitivity and specificity of the furosemide/fludrocortisone test which can
lead to an altered diagnostic algorithm for dRTA.

This study has two main objectives:

• to evaluate the prevalence of dRTA in pSS using the urinary acidification
test with FF and compare this against the gold standard test with AMCL.

• to evaluate whether a low BMD is more prevalent in patients with dRTA in pSS
compared to patients without dRTA in pSS

This study has one secondary objective:

• To calculate the sensitivity and specificity for the FF test to diagnose
dRTA.

The current study is designed as an observational study with invasive
measurements. All participants will be seen twice in the hospital, with minimal
one week in between. On the first day, all participants will undergo the AMCL
loading test and on the second day the FF test will be performed. During the
time they are in the hospital, a DEXA scan will be performed.

This study design provides us results of both urinary acidification tests
performed in our target population. Additionally, performing a DEXA scan in all
participants will give us information whether low BMD is more prevalent in pSS
patient with dRTA as compared to those without.

This project is expected to determine the prevalence of dRTA in pSS and its
major complication, which is low BMD. Many patients with pSS have complaints of
fatigue and generally feel unwell. The presence of dRTA may be a potentially
treatable explanation of these complaints in some patients. Additionally, the
clinical relevance of both tests will be calculated.
Prior to the study, if applicable, treatment with potassium citrate should be
stopped. The participants have to be hospitalized for two days. The urinary
acidification test with FF has no reported side-effects, but the acidification
test with AMCL can cause temporarily abdominal pain and nausea. The DEXA scan
has a negligible radiation load. Although the tests are safe, all participants
are insured for adverse events.