Lentiform fork sign in a patient with systemic lupus erythematosus

The “lentiform fork sign” is a rare MRI sign which affects the posterior limb of the internal capsule, the external capsule, and extends posteriorly to form a fork-like appearance. It has been reported exclusively in disorders with metabolic acidosis, such as uremic encephalopathy, mitochondrial disorders, methanol/ethylene glycol intoxication, etc. It is considered to represent vasogenic edema and is often reversible. We describe a 73-year old female with a 2-month history of rapidly deteriorating imbalance, bradykinesia, confusion, and disorientation. At examination, she was encephalopathic. She had a pyramidal and rigid-akinetic parkinsonian syndrome, with signs of polyneuropathy. MRI revealed the “lentiform fork sign”. She exhibited a high ANA titer, positive anti-dsDNA, anti-ENA, and anti-β2GPI-IgM antibodies, as well as positive cerebrospinal fluid IgG and albumin indices. No metabolic acidosis was recorded. A diagnosis of systemic lupus erythematosus (SLE) was established. She was treated initially with methylprednisolone, followed by hydroxychloroquine, with complete remission of her symptoms and disappearance of the “lentiform fork sign”. We present a case of a patient with SLE, harboring the “lentiform fork sign”, in the absence of metabolic acidosis. Differential diagnosis of the “lentiform fork sign” should be expanded to include autoimmune disorders, even in the absence of metabolic acidosis.