Arimoclomol in Sporadic Inclusion Body Myositis - Open Label Extension Trial

Inclusion Criteria: 1. Patient is able to comprehend and is willing to provide written informed consent and is capable and willing to comply with trial procedures. 2. Patient has completed the IBM4809 trial on treatment with Investigational Medicinal Product (IMP). Exclusion Criteria: 1. Known or suspected allergy or intolerance to arimoclomol or its constituents. 2. Exposure to any other investigational treatment within 30 days or \<5 half-lives of the baseline visit or taking part or planning to take part in another interventional trial. 3. Significant protocol deviation in the blinded IBM4809 trial based on the investigator's judgement in discussion with the medical monitor. 4. Women who are lactating or pregnant, or men or women unwilling to use a highly effective method of birth control if not surgically sterile (defined as bilateral tubal ligation, bilateral oophorectomy, or hysterectomy for women; vasectomy for men) for female participants until 4 weeks after last dose and for male participants up to 3 months after last dose. Premenopausal women must have a negative pregnancy test prior to dosing with trial medication. Acceptable methods of birth control are: * Hormonal methods associated with inhibition of ovulation such as oral, implantable, injectable, or transdermal contraceptives for a minimum of 1 full cycle (based on the patient's usual menstrual cycle period) before arimoclomol administration. * Total abstinence from sexual intercourse since the last menses before arimoclomol administration. (The reliability of sexual abstinence needs to be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. Periodic abstinence \[calendar, symptothermal, post-ovulation\] methods are not acceptable methods of contraception). * Intrauterine device (IUD) or intrauterine hormone-releasing system (IUS). 5. Any concurrent condition that in the investigator's opinion will significantly interfere with assessment of safety or efficacy. 6. Inability to comply with the protocol-specified procedures/evaluations and scheduled visits as per the investigator.