How should we interpret the lower lip biopsy finding in patients investigated for Sjögren's syndrome?

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Based upon case history alone, it might be difficult in individual cases to distinguish between the various systemic rheumatic diseases. Because a precise diagnosis is necessary in order to prescribe the most optimal therapy and way of living, (at least up to the time of introducing the use of biologic agents), it is important that rheumatologists know which tests and/or procedures to initiate. If the patient exhibits symmetric wrist and finger joint arthralgia with or without intermittently swollen joints, the 2 most common connective tissue diseases, primary Sjögren's syndrome (SS) or rheumatoid arthritis, might be suspected. Consultations by specialists in oral medicine, oral surgery, dental diseases, and ophthalmology are essential in obtaining information on the function of the main exocrine glands—the salivary and the lachrymal glands.

Figure 1.

In 1984, Daniels published the results of his pathologic findings of the small salivary glands obtained from 362 lower lip biopsies, evaluating a minimum of 5 lobules each (1). He concluded that a focus score > 1 per 4 mm2 tissue sample was indicative of SS. A focus was determined to be a collection of mononuclear cells with more than 50 lymphocytes/plasma cells and macrophages(1), either distributed around a salivary duct or perivascular. Due to the lack of other specific tests, the statement seemed so authoritative that soon the focus score was found in every classification criteria set for SS(2).

So what is new within the focus score? Let us examine the work of Brennan et al in this issue as an example of the progress occurring since 1984. From 1984–2000, Brennan et al retrospectively studied risk factors for positive minor salivary gland biopsies in patients referred with dry mouth and primary or secondary SS (3). Primary SS was defined as evidence of salivary and lachrymal dysfunction, the latter established if one objective test (rose bengal staining and/or Schirmer-I) gave an abnormal result, and keratoconjunctivitis sicca (KCS). Only those patients with a history of radiotherapy to the head and the neck were excluded from this study(3).

Although specific medication data were available, it was not extracted from the patient chart. Even though medication is known to give rise to dry mouth (and dry eyes?) medications were not an exclusion from the study (3). Therefore, we do not know the effect medications (including those having dry mouth as a side effect) had on the frequency of abnormal focus scores in patients, or on the background population involved.

During the initial period of the study, from 1984–1997, (13.7 years), Brennan et al evaluated 178 patients who exhibited “objective signs of eye dryness and/or autoimmune serology,” and had a minor salivary gland biopsy (3). The following factors were tested for positive predictor variables: 1) sex, KCS, and laboratory results (IgG, IgA, IgM; anti-SSA; anti-SSB, rheumatoid factor, and erythrocyte sedimentation rate); 2) both unstimulated and stimulated parotid flow measured by catheterization of the Stensen's duct where it penetrates the oral mucosa for X minutes; and 3) submandibular flow measured by collecting saliva from the mouth floor. In the second period of the study (1997–2000, 2.5 years), the 4 positive factors found (sex, KCS, IgG, and IgA) were tested against the results of the 111 lower lip biopsies that were performed during this period in all patients complaining of dry mouth(3). On average, the frequency of lower lip biopsy increased from 13/year to 44/year! The result of the second factor analysis (IgG measured as normal/abnormal), showed an association with the biopsy result. Further analysis showed that 55% of the patients with a diagnosis of SS had a normal IgG(3).

What about the influence of tobacco on the focus score? Late in the previous century, it was announced that patients who either were smokers or who had a history of smoking would have a reduced lower lip focus score. They were still considered to be SS patients because they had at least 2 other abnormal salivary gland functional test results as well as at least 2 abnormal lachrymal gland test results. More astonishing was the very strong correlation between focus score and the self-reported number of cigarettes smoked per week (4). Because an association between focus score and the serum presence of anti-SSA and/or anti-SSB antibodies exists, it was not surprising that cigarette-smoking data also correlated with anti-SSA and/or anti-SSB antibodies(4). Although the observation has been confirmed in another independent primary SS study(5) it is somewhat surprising that the subject was not addressed by Brennan et al, especially because the patients had a “clinical and laboratory examination” as well as a “complete diagnostic evaluation” at the NIH(3).

Will the lower lip biopsy procedure persist in the future? Certainly, yes, but with reduced frequency. The lower lip procedure is being used more often by SS specialists compared with other salivary dysfunction diagnostic procedures. It is inexpensive and fairly easy to perform if an experienced odontologist is at hand. However, the lower lip biopsy may be used less frequently in the future due to the fact that patients' wishes must be respected; and because an absence of post procedure dysesthesia, numbness, and minor pain cannot be absolutely guaranteed, an increasing number of patients will decline the procedure. Furthermore, surgeons cannot guarantee retrieval of at least 5 small salivary glands, and experience technical difficulties in 3–5% of the cases. Someday, if we can hopefully find a new test with almost 100% sensitivity and specificity, the lip biopsy procedure will not be needed for diagnostic purposes. Within epidemiology we have already been faced with such concerns, because several healthy controls have denied a lower lip biopsy. We must remember that under normal conditions only 2 lower lip biopsies can be performed on an individual, therefore the use of lower lip biopsy in clinical drug trials is not possible.

Are the results reliable (3)? According to a recent publication(6), it was found that rereading lower lip biopsies by experts changed the initial diagnosis in 53% of the cases—corresponding to the flip of a coin. Because rereading was not performed by any of the 8 authors in the Brennan et al study, we do not have an answer(3). However, it could be speculated that the reliability could be low because reporting of other equally important tests were well below the expected standard. The unit used for the Schirmer-I test was reported to be mm/minute, and the median values for those patients with a negative minor salivary gland biopsy to be 7 mm/minute (25th to 75th percentile, 3.5–13). Some readers will undoubtedly think that the procedure was performed for one minute only, not the recommended 5 minutes.

The authors are to be congratulated in that they stress that the Schirmer-I procedure was performed without anesthesia, which is different from the standard US procedure. They did, however, follow standard US procedure by having the patients keep their eyes open, instead of using the recommended procedure of placing a Whatmann paper laterally in the lower conjunctival sac and keeping it there with the eyes slightly closed for 5 minutes. Similar concerns can be raised with the technique of measuring saliva volume. The recommended time to measure unstimulated production of saliva is 15 minutes, and recommended time to measure stimulated production is 5 minutes.

To summarize, it is to be expected that the use of lower lip biopsy to determine focus score in small salivary glands for diagnostic purposes will decrease outside university studies whereas the frequency will, most probably, continue unchanged at studies conducted at universities. Tissue sections at these institutions will be studied for lymphocyte traffic, cytokines and chemokines, activation and deactivation of cell-surface receptors, autoantibody synthesis, regulation of nerve transmitters and signals, apoptosis, vascular permeability, aqua porin, and saliva production mechanism.

Is there anything more we can learn from the Brennan et al study? The reader must be his or her own judge, but at least in Europe there is a more balanced list between US and non-US references. Another concern, not specific to this publication, is the introduction of new laboratory techniques with other units of measure. The new methods may not necessarily be better within the field of rheumatology, and as correctly pointed out by the authors, may lead to bias with inconsistency over time (3). Few would have guessed that at NIH the traditional erythrocyte sedimentation rate has been replaced by the Vesmatic.

Is the IgG result unexpected? Not at all. In the introduction, Brennan et al report that an association between serum IgG and focus score is well known (3), and such reports/presentations have occurred since the start of the International SS Congress in 1986. Why do the anti-SSA and/or anti-SSB antibodies not emerge as the final predictive factor? Today, the group leader requires that a diagnosis of SS only can be made in patients with positive focus score and/or the presence of serum anti-SSA and/or anti-SSB antibodies(7). These quite opposite results have not been discussed.

Acknowledgements

Professor Åke Larsson and Tom Manthorpe are thanked for their assistance in the production of these comments.

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