The prevalence of DVT among men and individuals over 40 years was more than that among women and people below 40. In addition, the third important risk factor (after age and sex) was immobilization.
The regression model showed a significant difference between immobilization and coagulation disorders in patients with first and recurrent DVT. Although immobilization was more common among FDVT patients, stepwise regression showed a significant association between immobilization and RDVT (OR = 4.570). Moreover, hospitalization duration and swelling frequency were significantly less common in RDVT subjects. Kyrle et al. followed 826 patients for 36 months after the first DVT and observed the disease recurrence in 20% of men and 6% of women. Their results indicated a significant relationship between sex and disease recurrence (RR 3.6, 95% CI 2.3-5.5, P < 0.001).23
In a meta-analysis conducted on 7 prospective researches, Douketis et al. studied 2554 subjects who were followed for an average of 27.1 months and suggested that compared to women, men were 2.2 times more likely to experience a recurrent VTE after their first DVT. Even after adjusting the model based on HRT in women, recurrent DVT was 1.8 times more common among men.24
Unlike some previous studies, our findings did not suggest any relation between sex and DVT recurrence (maybe because this was a retrospective study conducted on patients with RDVT).
Cushman et al. studied the occurrence of DVT and pulmonary embolism in 21680 subjects over 45 years that participated in two cohort studies, namely Atherosclerosis Risk in Communities and the Cardiovascular Health Study. The subjects were followed for 7 years. First VTE rate was 1.92 out of 1000. The condition was more prevalent among men and its occurrence increased with age. The annual recurrence rate during the 2-year period after the first VTE was 7.7 and the only reason for the disease recurrence was cancer (RR 9.2, 95% CI 2.0-41.7).12
In a cohort study, Hansson et al. followed 738 patients with DVT for 3.7-8.8 years and found the cumulative incidence of recurrent VTE to be 21.5% in 5 years. Their multivariate survival analysis revealed proximal DVT, cancer and previous history of thromboembolism to be independent risk factors for the VTE recurrence. They did not find any significant relations between age, sex, antithrombotic treatment or immobilization and disease recurrence.19
In another study, White et al. followed 37000 patients with DVT for 6 months and suggested that DVT recurrence is related with age, cancer, surgeries and hospitalization duration.18
A clinical trial conducted by Schulman et al. followed 897 subjects, divided into two groups receiving vitamin antagonist for 6 weeks and 6 months for ten years, respectively. Regardless of the intervention group, disease recurrence was seen in 29.1% of all patients. This study found a significant association between disease recurrence and high age, being male, persistent risk factors especially venous insufficiency at baseline, proximal DVT, pulmonary embolism, and symptoms of impaired venous circulation disorder at the time of release.25
In 2005, Partsch reviewed the studies on acute DVT recurrence and reported that some studies suggested immobilization or restricted physical activity as important factors in disease recurrence. In addition, the same studies recommended walking accompanied with an appropriate compression on the involved site during the treatment period. His results indicated that immobilization, as one of Virchow's triad criteria, may cause venous stasis.26
Prandoni et al. conducted a study on 377 DVT patients and found recurrent DVT associated with immobilization. Similar to Partsch inference, they also suggested quick mobilization of the patients and increasing their physical activity after the first DVT as a good treatment method.3
Several studies conducted on the relation between DVT recurrence and its associated risk factors including age, sex, cancer, bone fractures, hip and knee surgeries, proximal DVT, immobilization and coagulation disorders. However, these studies were most prospective and included patients with FDVT. Unlike the mentioned researches, our study did not find any significant relation between RDVT and cancer, age, surgery, sex, and proximal DVT. However, our results revealed the strong effect of immobilization on RDVT. In addition, numerous studies suggested coagulation disorders to be one of the most important factors causing DVT, either for the first time or as a recurrent disease. We could not prove coagulopathy as a risk factor. The reason might have been the care individuals with a history of disorders paid to their treatment. In other words, the concurrence of such disorders and a DVT incidence caused the patients to commit to treatment. Therefore, to our surprise, coagulopathy actually appeared as a preventive factor. A further prospective study would be beneficial in clearly understanding the issue.
The high rate of intravenous (IV) drug abusers (8.3%) among the patients in the present study was also noticeable. Previous studies on drug addicts suggested DVT as a complication caused by drug abuse (especially IV drug abuse). Mohammadzadeh et al. studied 50 IV drug abusers in Northern Iran and indicated pseudo aneurysm with a frequency of 52% as the most common vascular complication among these subjects. DVT was the next common complication with a frequency of 18%.27
Yegane et al. studied the effect of surgery on 62 IV drug abusers complaining from tenderness and swelling in the groin region and noted a high rate of DVT (50%) among these patients.28
In a case-control study, Masoomi et al. compared DVT patients with healthy subjects in central Iran (Kerman). They showed that in the regression model, the crude effect of opium addiction on DVT was very strong (OR 4.25, 95% CI 2.6-6.9). However, the effect was eliminated after multivariate regression analysis (OR 0.56, 95% CI 0.1-3).29
Based on the results from the present study, increased physical activity is recommended to individuals with long periods of immobilization. If the patient is able to move after the first DVT, they are suggested to start mobilization quickly and to be physically active during long haul flights. Moreover, considering the relationship between coagulation disorders and disease recurrence, an appropriate antithrombotic treatment would be necessary.
This was a retrospective study based on the information that patients provided for their physicians. A prospective study can follow the patients with first DVT and exactly record the risk factors and treatment methods applied to determine their effects on disease recurrence. Another point to keep in mind is to educate IV drug abusers about methods preventing thrombosis and the associated complications.