The types of comorbidities found in patients with FM were similar to the ones in the control patients without FM. The most relevant differences were the higher number and the longer duration of the treatments found in patients with FM in this study.
Drugs for treating NS comorbidities, migraines, dizziness, gastric protectors and the use of analgesics were more common in patients with FM, as described in previous studies , but these clinical conditions are also commonly present in many patients without FM.
Drugs for treating potential severe comorbidities such as high blood pressure, hypothyroidism or high cholesterol levels were the same as in controls without FM showing that these types of comorbidities are not increased in FM patients. Similar findings were found in a recent systematic revision  where the presence of severe comorbidity in FM was analysed but no clear association was found.
However, drugs for treating mild comorbidities such as vitamin D or other vitamins, iron, folic, Q10 deficiencies, coeliac disease and lactose intolerance were found significantly more frequent in patients with FM. It is known that the prescription of these types of treatment depends on the facultative criteria and it is not usually based on clinical practice guidelines recommendations.
The difference between comorbidity and symptom is not well defined . Most drugs consumed by patients with FM are prescribed for treating symptoms that are inherent to the principal clinical picture of FM and for this reason they are not considered as comorbidities by some authors . Positive correlation found in this study between somatic symptoms and the number of drugs prescribed indicates that the more symptomatic the disease is the higher is the number of drugs prescribed.
For example, in rheumatoid arthritis the extra-articular manifestations are considered as clinical manifestations by some authors or as comorbidities by others . The treatment used to be almost the same. However, considering clinical manifestations as symptoms or as comorbidities in FM—a multisymptomatic disease—can have considerable consequences. In the first case, the main treatment of FM can be sufficient to improve symptoms but, in the second case, the probability of prescribing new drugs is high.
Separate treatment of clinical manifestations does not guarantee an improvement in the disease and may increase the risk of drug interactions and adverse events adding more clinical manifestations or aggravating them . Some studies have shown that some clinical manifestations such as dizziness—a common symptom in patients with FM—are positively correlated with the number of consumed drugs .
Positive correlation between the use of gastric protectors and the total drugs consumed by our patients probably indicate the need to add more drugs to prevent complications when many other treatments are already used. This clearly contributes to increase polymedication.
Opioids prescription in patients with FM has increased drastically over the past years. However, it is well known that opioid prescribing decision is not based only on patient–physician interaction but also on other factors that may explain the wide geographic variation found in some studies .
In our study, 13.6 % of patients with FM were taking major opioids and 74 % consumed benzodiazepines. Recently, it has been shown that combined consumption of these two drugs clearly increases the risk of serious interactions and can multiply by 15 the risk of death . Although there is no conclusive evidence against these two drugs in the treatment of FM, recent clinical guidelines in FM advise against their use by their deleterious adverse events [23, 24].
Psychiatric symptoms are very frequent and may be seen in two-thirds of the patients with FM, mostly depressive syndromes . The question of whether psychiatric symptoms precede the development of FM or appear along the course of the disease is frequently considered and does not have a good answer. But it is a very important issue when planning the treatment and follow-up of these patients.
Treatment with benzodiazepines and antidepressants has a shorter duration than with other drugs in this study, and they are prescribed when other comorbidities are already being treated. Additionally, 45 % of patients with a previous diagnosis of FM (group 1) versus 15 % of the patients with other diagnosis but fulfilling ACR criteria for FM (group 3) were also attended by psychiatrists. These data suggest that psychiatric comorbidity appears later in the course of the disease when other comorbidities and treatments have already started. It also means that in multisymptomatic patients an early psychological therapy focused on relaxation techniques, learning and acquisition of adequate coping strategies to manage initial somatic manifestations may be a great help to reduce NS drugs .
The appropriateness of the severe comorbidity treatments has shown that criteria for treatment were well established following clinical practice guidelines. However, for mild comorbidities, patients with FM received a greater number of treatments which were not well justified. This means that some drugs used for treating some clinical symptoms should be eliminated.
Patients’ demand for an efficient solution of their symptoms put a lot of pressure on the attending physician. In the absence of more appropriate resources—such as the psychological therapy mentioned before—the option of a drug prescription is an evident risk that should be avoided [27, 28].
Those patients who had not been previously diagnosed of FM but fulfilled ACR criteria (group 3) present some interesting features. The total number of drugs consumed, duration of treatments, presence of mild comorbidities and treatment appropriateness are the same as those of patients that do not have FM (group 2). Moreover, in this group, the analysis of the duration of the different treatments shows that benzodiazepines are the first drug prescribed for treating NS comorbidity.
This group is also interesting because it is composed of patients in the initial phases of the disease. On the one hand, they have many somatic symptoms and may be diagnosed of FM, but, on the other hand, they are not still treated with many drugs. Identifying these patients is very important in order to control the evolution of the disease and to avoid unnecessary use of drugs and their negative consequences.
In rheumatoid arthritis, some recommendations for treatment and control of the comorbidities have been recently established, due to the increased mortality risks . In the case of FM, establishing treatment criteria and recommendations for somatic symptoms and other comorbidities is also important, in this case to avoid polimedication, drug interactions and symptoms exacerbation.
This study has several limitations. The cross-sectional design of the study describes the situation of the patients compared with that of controls, but it does not shed light on the origin or the consequences of the problem. The lack of a control group with individuals of the general population does not allow a better evaluation of the drugs prescribed for treating comorbidities in these patients.
The fact that this study has been performed in only one centre specialized in FM management does not allow to generalize the results to other primary care centres or other types of patients.
The strong point of the paper is that its design and results allow a clear visualization of the FM spectrum, from mild clinical pictures with the possibility of early interventions and possible prevention up to severe cases.