Juvenile pSS is rare and its clinical symptoms and features are not well understood and are poorly defined [11,12,13,14]. In general, sicca symptoms are rarely observed in juvenile pSS patients. One reason for this absence may be that children are unable to accurately describe their symptoms . Additionally, xerostomia appears after salivary gland dysfunction has progressed to some extent. Therefore, it is unlikely that xerostomia will be seen in children, whose dysfunction is generally not advanced. Thus, the clinical symptoms differ between juvenile and adult SS [1, 11, 13].
Multicenter surveys and literature reviews have reported that the most common clinical symptom in juvenile pSS is recurrent parotitis [1,2,3,4]. However, recurrent parotitis is a common disorder in childhood, caused most often by viral or bacterial infections [11, 15]. In juvenile pSS, other common conditions have been reported, such as fever of unknown origin, erythema, joint pain, fatigue, and multiple dental caries [1,2,3,4, 12,13,14,15,16]. However, standardized specific diagnostic criteria have not been established for juvenile pSS [4, 13, 15, 17]. The lack of specific diagnostic criteria in children makes juvenile pSS poorly known and probably underdiagnosed [4, 11, 13, 14]. The early diagnosis of juvenile pSS on the basis of clinical manifestations is challenging.
Biopsy of the labial glands is important in the diagnostic evaluation of SS patients . However, this invasive examination is difficult to perform in all juvenile SS patients. Therefore, it is necessary to establish more sensitive child-specific diagnostic criteria for the unique patterns of early stages of the disease.
We propose the utility of noninvasive imaging examinations such as MRI and US. Although MRI and US findings are not currently included in the diagnostic criteria for SS, these imaging modalities have an important role in the evaluation of salivary glands and improve the diagnostic performance in adult SS [5,6,7, 19,20,21]. The usefulness of these imaging examinations in juvenile pSS is demonstrated in this study. Therefore, these imaging examinations are expected to become a useful noninvasive substitute for labial gland biopsy in both juvenile and adult SS. In addition, because these imaging modalities are noninvasive, they can be performed repeatedly. SS is an insidious and chronic disease; therefore, it is important to diagnose patients in the early stages and to follow them for a long time . Follow-up imaging examinations are useful to assess the degree of progression in every salivary gland (parotid, submandibular, and sublingual glands).
Kimura et al. reported that fat degeneration of the glands is a characteristic finding on MR images in juvenile SS . However, there were no findings suggestive of fat degeneration in this case. Fat degeneration is a conspicuous finding with progression of SS . Because most juvenile SS patients are considered to be in the early stage of SS, it is conceivable that they are less likely to have associated fat degeneration. Fat degeneration is not always seen in the early stage of adult SS. Instead, multiple dispersed high-intensity spots in the parenchyma of the bilateral parotid glands are often observed on fat-suppressed T2-weighted MR images [5, 6], as in this case (Fig. 1e). The high-intensity spots on fat-suppressed T2-weighted MR images almost coincided with sialoectasia on MR sialography of the bilateral parotid glands [5, 6] (Fig. 1 e, f, g). Therefore, in juvenile SS, which is generally considered to be an early stage of SS, we think that multiple dispersed high-intensity spots in the bilateral parotid gland parenchyma on fat-suppressed T2-weighted MR images and/or sialoectatic change in the bilateral parotid glands on MR sialography are more characteristic findings than fat degeneration. However, further investigation with increased numbers of juvenile SS cases is needed to confirm this hypothesis.
Multiple dispersed high-intensity spots on fat-suppressed T2-weighted MR images and/or sialoectasia on MR sialography in the parotid gland parenchyma are also found in juvenile recurrent parotitis. However, the findings are unilateral in most cases of recurrent parotitis, whereas they are bilateral in SS, a difference that is useful in discriminating between the two diseases . In this case, the findings were present in the bilateral parotid glands and there were no clinical signs of suspected parotitis. Therefore, parotitis was excluded and SS was suspected.
Additional US examinations showed findings suggestive of SS not only in the bilateral parotid glands but also in the bilateral submandibular glands (Fig. 2a-d). However, MRI did not reveal any findings of SS in the submandibular glands. US is a quick and inexpensive procedure compared with MRI and does not require patient sedation. Therefore, we think US is more appropriate than MRI for diagnosing juvenile SS, unless diagnosis of a ranula is necessary [11, 14].
Ranulae are clinically subdivided into simple (intraoral) and plunging (cervical) according to the extent of the pseudocyst. The simple ranula is present within the sublingual space, whereas the plunging ranula extends beyond the mylohyoid muscle to the submandibular space and adjacent structures in the neck, as in our present case (Fig. 1b) [8, 23, 24].
Ranulae most frequently occur in patients under the age of 30 years and rarely occur in young children . However, Than et al. reported many pediatric ranula cases. According to that report, simple ranulae are more common and occur at a younger average age than plunging ranulae .
Ranulae are caused by extravasation of saliva resulting from damage to the sublingual glands and/or obstruction of their ducts. The pathological feature of SS is periductal lymphocytic infiltration; the resulting damage to the duct is presumed to induce the extravasation of saliva and thus mucus accumulation . Therefore, the ranula is likely to be an important clinical sign of SS. Although there are few reports on the relationship between SS and ranula [2, 9, 10], Sato et al. reported that extravasation of saliva from fragile ducts often occurs only in the early stages of SS . Ranulae are less likely to develop in advanced stages because there is insufficient saliva to form a ranula when there is acinar atrophy and loss resulting from chronic lymphocyte aggregation . Therefore, a ranula is one of the characteristic symptoms of early SS.
Our case series study revealed that 11 of the 51 patients with ranula had findings suggestive of SS, indicating that SS may be accompanied by ranula in both adults and children. In addition, the age of ranula development in patients suspected of having SS was relatively young, and the SS stage of the patients who underwent MRI at our hospital was not advanced (Table 1). This finding suggests that ranulae occur in the early stages rather than in the advanced stages of SS, as Sato et al. stated .
In some cases, as in the juvenile pSS case presented here, a ranula may be the only clinical sign that leads to early detection of SS. Therefore, patients with ranulae, whether adults or children, should undergo careful assessment of not only the sublingual glands but also the parotid and submandibular glands with MRI and/or US to investigate possible SS.
In addition, we recommend the inclusion of imaging examinations in the diagnostic criteria for juvenile and adult SS to facilitate diagnosis at an earlier stage of the disease.
Currently, diagnosis of juvenile pSS is more difficult than that of juvenile sSS or adult SS. However, if imaging examinations such as MRI and/or US are used to diagnose SS, juvenile pSS can be diagnosed earlier. Earlier diagnosis will allow earlier initiation of treatment and prevention of progression in the exocrine glands and complications in other organs.