Reader response: Clinical Reasoning: A 45-year-old man with progressive insomnia and psychiatric and motor symptoms
CarlosSinger, Professor of Neurology, University of Maimi
JasonMargolesky, Assistant Professor of Neurology, University of Miami
Submitted March 30, 2020
We read with interest the article by Lima et al.1 The authors report a case of fatal familial insomnia (FFI) with initial laboratory findings suggestive of autoimmune encephalitis, which failed to respond to immunotherapy. Postmortem revealed immunoreactivity of the prion protein restricted to neurons in the thalamus and genetic testing detected a D178N/129M mutation in the prion protein gene confirming the diagnosis of FFI.
We were puzzled by a reported finding in the CSF where the authors state that the “immunoglobulin G index was elevated at 696 mg/L.” Since CSF IgG index is not expressed in mg/L, we request clarification of this finding. We suspect that a CSF IgG concentration was erroneously reported as an index. This value would need to be compared to the contemporaneous serum concentration to calculate the CSF IgG index. Assuming the index was elevated (>0.80), the authors would need to discuss the presence of such an abnormal finding in a case of prion disease.
Disclosure
The authors report no relevant disclosures. Contact journal@neurology.org for full disclosures.
Reference
Lima JEE, Youn TS, Robinson C, et al. Clinical Reasoning: A 45-year-old man with progressive insomnia and psychiatric and motor symptoms. Neurology 2020;94:e1213–e1218.
We read with interest the article by Lima et al.1 The authors report a case of fatal familial insomnia (FFI) with initial laboratory findings suggestive of autoimmune encephalitis, which failed to respond to immunotherapy. Postmortem revealed immunoreactivity of the prion protein restricted to neurons in the thalamus and genetic testing detected a D178N/129M mutation in the prion protein gene confirming the diagnosis of FFI.
We were puzzled by a reported finding in the CSF where the authors state that the “immunoglobulin G index was elevated at 696 mg/L.” Since CSF IgG index is not expressed in mg/L, we request clarification of this finding. We suspect that a CSF IgG concentration was erroneously reported as an index. This value would need to be compared to the contemporaneous serum concentration to calculate the CSF IgG index. Assuming the index was elevated (>0.80), the authors would need to discuss the presence of such an abnormal finding in a case of prion disease.
Disclosure
The authors report no relevant disclosures. Contact journal@neurology.org for full disclosures.
Reference