Herein we describe 10 cases from three centers with symptoms involved the abdomen, 2 of which were isolated to the abdomen, 1 with chest involved and 7 of which included legs. The technical definition of RLS requires leg involvement but does not exclude concurrent extra-leg involvement, therefore our cases with isolated abdominal involvement do not meet criteria for RLS, yet responded similarly to treatment, suggesting similar pathophysiology. Abdomen involvement in RLS is not common. In our previous single center study, we included 359 primary RLS patients and found a total of 61 (17%) patients had extra body parts involvement beyond the legs, only 5 patients (1.4%) of which presented abdomen involvement and are included in this study.
Previous studies have revealed that there is a female gender preponderance in RLS patients. In our Chinese population, women have almost twice as many cases as men [13, 14]. However, cases of restless abdomen reported so far have mostly male [12, 15, 16]. In contrast, our study found only two male patients (20%). A number of studies have found that the higher prevalence of RLS in women may be relevant to hormonal changes in the body [17–19]. However, to the best of our knowledge, no one has studied the sexual orientation of restless abdomen. Whether a gender bias exists in cases of restless abdomen remains unclear. The difference between our reported cases and those previously reported restless abdomen may be due to 1) the restless abdomen cases don’t have a clear gender preference as a matter of fact. 2) Racial differences between ever reported cases and cases herein. 3) Random chance, given the small sample size. But it still reminds us to pay more attention to men’s sensations during later work.
Compared to our previous study in the general RLS population , restless abdomen cases had a higher age at symptom onset (51.3± 21.18 vs. 38.0 ±15.3 years).Since early onset of RLS correlates with the likelihood of a positive family history of RLS, the relatively older age at onset in abdominal RLS compared to the general RLS population is consistent with this result, suggesting more influence of non-genetic causes.
All the patients we report here had abnormal sensation that led to poor sleep. This feature is consistent with several previously reported cases. These patients always suffered from severe insomnia but may have sought care from a gastroenterologists rather than neurologist or sleep specialist [12, 20]. Therefore, it is important for neurologists, especially those who work in sleep clinics, to be able to identify patients with restless abdomen.
Augmentation can increase anatomy of RLS involvement but only 2 of our subjects were on dopaminergics at abdominal symptom onset for 4 and 3 years, and neither demonstrated other evidence of augmentation (Table 3).
Although the exact pathophysiological mechanism of RLS is unknown, brain iron insufficiency and dysfunction of the dopaminergic system have been proposed. Combining the results of previous studies, we suppose that striatonigral and/or hypothalamic dopaminergic involvement might have involved a projection to the T7–T12 thoracic spinal segments, resulting in abnormal sensations in the abdomen.
Restless abdomen can be considered as a part of the phenotypic spectrum of RLS or a separate variant of RLS. Our 7 cases had discomfort in abdomen accompanied with legs discomfort and satisfied the diagnostic criteria for RLS. These characteristics support that cases here are a part of the phenotypic spectrum of RLS. However, compared to RLS in our general population, this population was older at onset, lacked a family history of RLS suggesting a phenotypic variant of RLS. Therefore, considering that distribution of the restlessness of our 8 cases is not restricted to the abdomen and these patients with abdominal symptoms responded to dopaminergics, we can’t rule out the possibility that these 8 cases here are a part of the phenotypic spectrum of RLS.
There are some limitations in our research. Firstly, it has been reported in the past literature that such patients have a high incidence of PLMS , but we did not ask about this in detail when collecting the history. Furthermore, since most of them were outpatient patients, no PSG data were available. Secondly, there is a lack of follow-up data such as IRLSRS, HAMD, and HAMA and so on. Nevertheless, we feel this report should add to recognition of an unusual phenotype which can be successfully treated after correct diagnosis.