## 1 Introduction  
Musculoskeletal disorders (MSDs) represent one of the major health problems worldwide for their high prevalence, impact on the quality of life (QoL) and the increased risk of motor disability. The recent analysis of Global Burden of Disease (GBD) data showed that approximately 1.71 billion people globally have MSDs and that these conditions constitute the highest cause in terms of years lived with disability (YLDs) [1, 2]. Among them, rheumatic diseases contribute to the largest proportion of musculoskeletal burden, with higher prevalence for five major conditions: Low-Back Pain (LBP), Osteoarthritis (OA), Neck Pain, Rheumatoid Arthritis (RA), and Gout [3].  
The management of rheumatic pathologies includes a combination of pharmacological and non-pharmacological interventions to reduce pain, improve functional limitations and ameliorate the QoL. International clinical guidelines generally recommend and highlight the rehabilitation protocols in the complex multimodal treatment of these conditions [4].  
Nowadays, one of the most frequently prescribed non-pharmacological treatments in the management of rheumatic diseases is Balneotherapy (BT) [5]. BT is a complementary modality using mineral waters from natural springs, for the preventive, therapeutic, and rehabilitative treatment of various illnesses. It includes a broad spectrum of interventions, such as bathing, applications of peloid, dry peloid therapy, gas bath, drinking, inhalation, irrigations, etc [6].  
The BT modalities most frequently used for rheumatic diseases are thermal baths and mud applications. Thermal baths require patient immersion in a tub or pool containing thermal water; a cycle usually ranges from 10 to 20 sessions and can also include hydro-massage. Mud therapy consists of applying a layer of mud heated to 45-50\({}^{\circ}\), generally for 20 min.  
BT can be combined with different treatment modalities, such as massage, exercise, physical therapy, health education, diet, etc. (Spa therapy) [6]. Furthermore, it is possible to perform a rehabilitative program with hydrokinesitrapy in thermal water with a faster recovery [7; 8; 9].  
A number of randomized clinical trials, meta-analyses and systematic reviews showed a positive effect of BT and Spa therapy on pain, function and QoL in patients with LBP, OA and Fibromyalgia Syndrome (FMS) [10; 11; 12]. However, the available evidence concerning the potential beneficial role of BT in combination with rehabilitation protocols in rheumatic diseases is still sparse.  
Additionally, the variety of scientific literature often does not facilitate the review analysis, not only because of the large number of papers but even of the inhomogeneity of the methods and the terms used for defining a disease or a medical intervention. For these reasons, support can come from a wide analysis of the lexicon used in the papers. Recently, we have proposed a method of lexical network based on graph-theory (LENGTH), able to highlight the association among the papers and a list of selected words. The method can also represent the importance of a word or a paper in the network. Hence, it can be used for supporting the paper selection for further review. In a few words, with the LENGTH approach, we performed a two-step analysis. First, we evaluated the most common words conveying meaning about the diseases, the clinical conditions, the outcome measures, the balneotherapy and the rehabilitation and their relationships with the papers. After this first analysis, we used the methods to perform an initial selection of the papers for the review.  
We, therefore, aim to review the highest evidence provided by published controlled trials to investigate the clinical effect of spa therapy for rheumatic diseases, with particular attention to association protocols between BT modalities and therapeutic exercise.