Diagnosis and Treatment of Abductor Hallucis Focal Dystonia With Botulinum Toxin Injection: A Case Presentation

Abstract

treatment. Focal dystonia is a rare neurologic condition that often limits function and is charac terized by involuntary muscle contraction in a non velocity dependent manner. In the majority of cases, an underlying cause remains unclear. The term describes a heterogenous set of conditions that can affect almost any location in the body, including the cervical musculature, oromandibular and laryngeal muscles, and the muscles of the extremities. The incidence is estimated at 24 per million per year [3] and occurs most commonly in men [4]. The incidence of upper extremity focal dystonia appears to be much higher in professionals who perform skilled tasks with their hands, such as musicians, dentists, surgeons, and watchmakers. CASE PRESENTATION An 81 year old man was referred to our rehabilitation clinic with a chief concern of severe right hallux varus deformity and an associated abnormal gait pattern. He first noticed this 15 years before presentation and acknowledged its progression over time. He also had right medial knee pain with ambulation. The patient had a pair of custom shoes with an oversized medial aspect of the toe box to accommodate his toe deformity. Other than these custom shoes, he had not undergone any other treatment. He denied any history of stroke or upper motor neuron disorder. There was no history of traumatic foot or toe injury. Medical and surgical histories were negative for foot trauma or surgery, contralateral joint deformity, or movement disorder. Pertinent family history was a daughter with a similar deformity. Physical examination demonstrated a right hallux varus with an abduction angle of 58 � when sitting (Figure 1) and firm muscular resistance appreciated with slow passive adduction of the great toe. This deformity was accentuated when standing, with a relative increase in abduction angle. There was no dystonia appreciated in the foot or the ankle. Neurologic examination was otherwise normal. Gait with a single point cane in the left hand was wide based, with pronounced external rotation of the right foot. A radiograph of the foot demonstrated medial subluxation of the first proximal phalanx with respect to the first metatarsal head. Given the physical examination finding of firm muscular resistance with slow passive adduction, electromyography (EMG) assessment of the right abductor hallucis was performed. The EMG demonstrated abnormal involuntary dystonic activity (Figure 2). This was presumed to be the cause of the patient’s great toe deformity. Botu linum toxin injection is indicated to reduce dystonic activity at this muscle [5]. After