The CEAP classification revised in 2020 classifies chronic venous disease into C (clinical manifestation), E (etiology), A (anatomic distribution), and P (pathophysiology). Among them, C was subdivided into categories C0-C6, and C0 was defined as “No visible or palpable signs of venous disease” (1).

The abovementioned CEAP classification, C0sEnAnPn, can be considered an objective situation without venous disease. However, since it relies on the patient’s subjective symptoms, scientific evidence of them is inevitably lacking and may lead to treatment confusion (2).

C0sEnAnPn patients were mentioned in several studies before the CEAP classification was developed in the mid-1980s, and the diagnosis of these patients in each study varied as follows (2-4):

• Functional phlebopathy

• Functional chronic venous disease (FCVD)

• Varicose symptoms without varicose vein

• Hypotonic phlebopathy

• Phlebostatic syndrome

The prevalence of FCVD according to a few studies is reportedly 13.9∼19.7% in the general population (3-6): 13∼23% in the Polish Study; 15% in the San Diego Vein Study; 19.7% in the Belgium and Luxemburg subgroup of the Vein Consult Program; and >80% in the Vein Consult Program (of the latter, 20% were in the C0 category).

There are four types of epidemiology in the literature (2,3):

1. Hypotonic phlebopathy (HP) with subjective symptoms always present. This condition accounted for 26.83% of total HP cases;

2. Latent HP with subjective symptoms was referred intermittently (spring, summer, pregnancy, hard upright work). This condition accounted for 27.43% of the total number of HP cases;

3. Enhanced HP with subjective symptoms is continuously present during the examination period but occasionally in the past and is related to an identifiable cause, accounting for 29.89% of the total number of HP cases; and

4. Senile HP with subjective symptoms have been continuously documented since the sixth decade and never or occasionally in the past, accounting for 15.89% of the total number of HP cases.

The symptoms of FCVD primarily include heavy legs (74.39%), nighttime resting cramps, restless leg syndrome (29.26%), numbness, a burning sensation, achiness, and swelling (2,3).

The risk factors include family history (42.07%), obesity (37.19%), and constipation (29.26%). Hemodialysis and pregnancy are significant risk factors.

The scientific cause of these symptoms is venous wall tension caused by venous dilatation (prolonged standing position in a normal subject or venous incompetence in ill subjects) and hypoxia of the tunica media of the venous wall due to alteration of the vasa vasorum (2,7). These processes are triggered and modulated by various inflamma-tory cytokines (8). There is much evidence that the symptoms of FCVD improve greatly with conservative treatment that can reduce inflammatory reactions, including venoactive drugs (2,8,9) and compression therapy (10).

In 2016, the SYM Vein Consensus statement developed under the auspices of the European Venous Forum mentioned the pathophysiology, evaluation, and treatment of FCVD (2,11). The practical guidelines of the International Union of Angiology (IUA) suggested its pathophysiology, evaluation, and treatment according to scientific evidence in 2020 (12).

According to the practical guidelines of the IUA in 2020, treatments for FCVD can be summarized as follows (12):

• Exclusion of non-venous cause of symptoms

• Adaptation of lifestyle

• Venoactive drugs

• Topical venoactive drugs and topical heparinoids

• Medical elastic stocking (ankle pressure 15∼20 mmHg)

The Vein Consult Program in 2012 reported that only 13% of C0 patients received lifestyle advice, while 8% were prescribed venoactive drugs (13). Due to a lack of awareness about C0 in the clinical field, many FCVD patients may be undertreated (13) or overtreated (14).

Although FCVD affects up to 20% of the general population, patients with FCVD are generally poorly treated. Given the inflammatory nature of CVD, we speculate that noninvasive treatment modalities to reduce inflammation may effectively control these symptoms.