Could botulinum toxin be a treatment for functional popliteal artery entrapment syndrome? A preliminary study

Abstract

Functional popliteal artery entrapment syndrome (FPAES) is an uncommon cause of exercise-induced leg pain. Contrary to the anatomic type, there is no anatomical abnormality: entrapment is caused by hypertrophic gastrocnemius muscles (GCM). Even though arterial compression is purely functional, a surgical arteriolysis of popliteal artery is often proposed, in order to release the artery from adjacent structures. It is sometimes associated with myotomy. Studies on surgical treatment lack for cases. We hypothesize that botulinum toxin A (BoNT-A) injections in GCM could improve GCM-artery impingement by inducing localized and partial muscular atrophy and hypotonia. This retrospective study included patients with FPAES treated with BoNT-A. Clinical exam, ankle brachial pressure index after exercise, provocative tests in plantar or dorsal flexion of the ankle (Doppler ultrasonography, computed tomography or magnetic resonance angiography) were used for diagnostic. Other causes of leg pain were systematically excluded with further investigations, such as compartment pressure after exercise, low back and leg imagery. BoNT-A was injected in the proximal third of both heads of GCM, in two sites for each head, after location of the muscles by electrical stimulation. Investigations with provocative maneuvers were done after treatment. Eight patients (fourteen limbs) aged between 17 and 54 years old were included. One patient had previously unsuccessfully been treated by surgery. Mean follow up was 22.1 ± 21.2 months (6–74). Five patients had resolution of symptoms, during 70.6 ± 74.3 weeks (17–216). Two patients are currently still asymptomatic. Three patients relapsed. Adverse events were moderate systemic events (two patients) and subjective muscular weakness (two patients). Ankle brachial index, Doppler ultrasonography or tomography angiography improved or normalized in three patients, all successfully treated. Long-lasting resolution of symptoms in five patients could indicate that BoNT-A injections reduce functional compression. However, treatment failed in three patients. Continuation of the study with more patients may indicate whether BoNT-A injections could be a treatment of FPAES, which has no appropriate treatment as of today.