Intervention: Denintuzumab mafodotin
Trial phase: Phase 2
SMILES: CCC(C)C(C(CC(=O)N1CCCC1C(OC)C(C)C(=O)NC(Cc1ccccc1)C(=O)O)OC)N(C)C(=O)C(NC(=O)C(C(C)C)N(C)C(=O)CCCCCN1C(=O)CC(SCC(N)C(=O)O)C1=O)C(C)C
Sex: All
Age groups: Child | Adult | Older Adult
Healthy volunteers: No
Participants at risk: 10
Group description: The study will include a total 20 individuals. Subjects will be randomized equally to treatment or placebo. Treatment will consist of IVIG administered at an initial dose of 2 grams/kg over 2 days followed by 1 gram/kg over 1 day every 3 weeks for a total of 6 treatments

Intravenous immunoglobulin: Gamunex-C [immune globulin injection (human) 10% caprylate/chromatography purified] is a sterile solution of human immune globulin protein.
Eligibility criteria:
Inclusion Criteria:

Patient with clinically evident and biopsy proven pure small fiber neuropathy as evidenced by reduced intra-epidermal nerve fiber density seen on skin biopsy using PGP 9.5 as the immunostain.
Patients must have a baseline pain score on a VAS scale of Greater or equal to 4/10
Patients must have elevated titers of autoantibodies to TS-HDS or FFR3 as measured in Dr Alan Pestronk's lab at Washington University in St Louis.

Exclusion Criteria:

Any other known cause for small fiber neuropathy other than the presence of the elevated titers of auto-antibodies. For example patients with diabetes, HIV, Sjogrens, Vitamin deficiency etc.
Patients with generalized, severe musculoskeletal conditions other than SFN that prevent a sufficient assessment of the patient by the physician
Cardiac insufficiency (New York Heart Association III/IV), cardiomyopathy, significant cardiac dysrhythmia requiring treatment, unstable or advanced ischemic heart disease).
Severe liver disease (ALAT 3x > normal value).
Severe kidney disease (creatinine 1.5x > normal value).
Known hepatitis B, hepatitis C or HIV infection.
Patients with a history of deep vein thrombosis (DVT) within the last year prior to baseline visit or pulmonary embolism ever; patients with susceptibility to embolism or deep vein thrombosis.
Body mass index (BMI) ≥40 kg/m2.
Medical conditions whose symptoms and effects could alter protein catabolism and/or IgG utilization (e.g. protein-losing enteropathies, nephrotic syndrome).
Known IgA deficiency with antibodies to IgA.
History of hypersensitivity, anaphylaxis or severe systemic response to immuno-globulin, blood or plasma derived products, or any component of Gamunex.
Known blood hyperviscosity, or other hypercoagulable states.
Use of IgG products within six months prior to enrolment.
Use of other blood or plasma-derived products within three months prior to enrollment.
Patients with a history of drug or alcohol abuse within the past five years prior to enrollment.
Patients unable or unwilling to understand or comply with the study protocol
Participating in another interventional clinical study with investigational treatment within three months prior to enrollment.
Women who are breast feeding, pregnant, or planning to become pregnant, or are unwilling to use an effective birth control method (such as implants, injectable, combined oral contraceptives, some intrauterine devices (IUDs), sexual abstinence or vasectomized partner) while on study.