• Efficacy: MAS, Physician's Rating Scale (PRS), speed of gait, Clinical Global Impression (CGI) Safety: Adverse events, clinical laboratory tests, pulse rate, blood pressure, 12-lead ECG
• Change from baseline in the MAS ankle score
• Change from baseline in speed of gait
• Global impression of therapeutic benefit of GSK1358820 to rehabilitation if any change is made to permissible concomitant rehabilitation therapy during the open-label phase.
• Change from baseline in PRS score
• Change from baseline in CGI score

• Efficacy:
• MAS, Physician's Rating Scale (PRS), speed of gait, Clinical Global Impression (CGI)
• Safety:
• Adverse events, clinical laboratory tests, pulse rate, blood pressure, 12-lead ECG

This is a study to confirm the superior efficacy of GSK1358820 over placebo in patients with equinus deformity associated with post-stroke lower limb spasticity using the Modified Ashworth Scale (MAS) ankle score.

Inclusion Criteria:

• Subjects eligible for enrollment in the study must meet all of the following criteria:
• Patients with lower limb spasticity who are at least 6 months post-stroke and present with equinus deformity (plantar flexion of the ankle) at the start of double-blind phase (Visit 2).
• Patients with MAS ankle score of ≥ 3 at the start of double-blind phase (Visit 2).
• Male or female between 20 and 80 years of age at the time of informed consent. For males, only those who can practice contraception during the study period are eligible.
• ≥ 50kg in weight at the start of double-blind phase (Visit 2).
• Inpatient or outpatient; however, the hospitalization status must remain unchanged during the double-blind phase. NOTE: Subjects may be hospitalized for ≤10 days after injection during the treatment period.
• Written informed consent from the subject him/herself. If the subject's signature is not legible, the attendance of a witness is required.

Exclusion Criteria:

• A subject will not be eligible for inclusion in this study if any of the following criteria apply:
• Bilateral hemiplegia or quadriplegia.
• Presence of fixed contractures of the ankle (absence of range of motion).
• Profound atrophy of the muscles to be injected.
• Previous surgical intervention, phenol block, ethanol block, or MAB for ankle spasticity.
• Casting of the study lower limb within 3 months prior to the start of double-blind phase (Visit 2).
• Current treatment with intrathecal baclofen.
• Use of peripheral muscle relaxants (dantrolene sodium, suxamethonium chloride, pancuronium bromide, vecuronium bromide).
• Concurrent use of antibiotics that interfere with neuromuscular transmission, such as aminoglycoside antibiotics (e.g., streptomycin sulfate, kanamycin sulfate, gentamicin sulfate, neomycin sulphate, spectinomycin hydrochloride), polypeptide antibiotics (e.g., polymixin B sulfate), lincomycin antibiotics (e.g., lincomycin hydrochloride, clindamycin), and enviomycin sulfate.
• Previous or current botulinum toxin therapy of any serotype.
• Diagnosis of systemic neuromuscular disorders (e.g., myasthenia gravis, Lambert-Eaton syndrome, amyotrophic lateral sclerosis).
• Females who are pregnant, nursing, may be pregnant, or planning a pregnancy during the study period.
• Known allergy or hypersensitivity to any ingredient of study medication (e.g., human serum albumin).
• Presence of psychiatric disorder or impairment of intellectual function that may interfere with the subject's ability to give informed consent or the conduct of the study.
• Bedridden patients.
• Presence of clinically unstable severe cardiovascular disease.
• Presence of clinically significant severe renal or hepatic disease.
• Infection or dermatological condition at the proposed injection sites.
• Previous or planned participation in another clinical study (including the upper limb spasticity study of GSK1358820) within 6 months prior to the start of double-blind phase (Visit 2).
• Others whom the investigator or sub investigator considers not eligible for the study.