Differential Diagnosis for Paraneoplastic Antibody Causing Proximal Weakness and Optic Neuritis
- Single most likely diagnosis:
- CRMP-5 (Collapsin Response Mediator Protein 5) antibody: This antibody is associated with various paraneoplastic neurological disorders, including proximal weakness and optic neuritis, often in the context of small cell lung cancer.
- Other Likely diagnoses:
- Anti-Hu antibody: While more commonly associated with sensory neuropathy and cerebellar ataxia, it can also cause proximal weakness and, less frequently, optic neuritis, particularly in the context of small cell lung cancer.
- Anti-Ma2 antibody: This antibody can cause a range of neurological symptoms, including proximal weakness and optic neuritis, particularly in the context of testicular cancer or other tumors.
- Do Not Miss diagnoses:
- NMO (Neuromyelitis Optica) antibody (AQP4-IgG): Although not strictly a paraneoplastic antibody, NMO can cause optic neuritis and, in some cases, proximal weakness, and is crucial to diagnose due to its treatment implications and potential association with certain cancers.
- Rare diagnoses:
- Anti-amphiphysin antibody: This is a rare paraneoplastic antibody that can cause a variety of neurological symptoms, including proximal weakness and, less commonly, optic neuritis, often in association with breast cancer.
- Anti-GAD (Glutamic Acid Decarboxylase) antibody: While primarily associated with stiff person syndrome, it can also cause proximal weakness and, in rare instances, optic neuritis, with or without an underlying cancer.