Froin syndrome (FS) is characterized by a combination of cerebrospinal fluid (CSF) xanthochromia, elevated protein levels, and hypercoagulability. FS can lead to increased intracranial pressure and may cause visual loss due to papilledema. FS was first described by Georges Froin in 1910 after performing a lumbar puncture on a patient with syphilitic meningitis. 
FS occurs following processes that affect normal CSF flow (e.g., meningeal irritation and inflammation or spinal cord obstruction by tumors), infection and abscess, degenerative stenosis, or disc herniations. Meningeal inflammation can be caused by viral and bacterial infections and can lead to increased CSF protein levels. These inflammatory and obstructive processes contribute to the stagnation of the CSF within the thecal sac and interruption of CSF absorption by the arachnoid granulations. The disruption of CSF reabsorption subsequently increases transudation which results in hyperproteinosis and hypercoagulation. Elevated CSF bilirubin and albumin produces a characteristic yellow (xanthochromic) color of the CSF. 
In FS, CSF protein levels can be elevated in the range of 75 - 500 mg/dL (normal values of 15 - 45 mg/dL) due to infectious causes but may increase to over 500 mg/dL in cases with spinal obstruction. Spinal tumors specifically can lead to transudation or exudation of protein into the CSF from the tumor and can cause break down of the blood brain barrier.  Breakdown of the blood brain barrier, CSF stagnation, and CSF proteinosis result in obstruction of CSF outflow and increased intracranial pressure.
The most common symptoms of FS are moderate to severe back pain that is often unresponsive to conventional treatments, progressive bilateral asymmetric lower extremity sensory deficits, weakness, and brisk or absent lower extremity reflexes.  Symptoms of increased intracranial pressure (ICP) can include headaches worse with positional changes, nausea, vomiting, and pulsatile tinnitus.
Increased CSF protein levels in Froin Syndrome often produce papilledema. Transient visual obscurations, horizontal binocular diplopia due to non-localizing sixth nerve palsy, and visual field loss may also occur in FS. In later-stages optic atrophy may develop secondary to chronic papilledema.
The conventional work up for increased ICP including patients with papilledema is cranial imaging (e.g., magnetic resonance imaging (MRI) with MR venogram)). Lumbar puncture is then performed and can confirm increased ICP on opening pressure and abnormal CSF indices. In cases with elevated CSF protein (with or without spine symptoms) spinal imaging should be considered. Interestingly, “dry tap” (failure to obtain CSF during an LP) may occur due to an obstruction from a spinal cord mass leading to delay in diagnosis and treatment. A dry tap or elevated CSF protein should prompt spinal imaging for suspected FS.
- Meningitis 
- Spinal Tumor 
- Spinal epidural abscess 
- Multiple Myeloma 
- Trauma 
- Guillain-Barre Syndrome 
A summary on Froin Syndrome by Dr. Andrew G. Lee can be accessed here:
The management of FS should be directed at the underlying etiology (e.g., antibiotics for meningitis, steroids for inflammation, surgery for spine tumors). Papilledema may require medical (acetazolamide) or surgical therapy (e.g., optic nerve sheath fenestration, CSF diversion procedures). Acute visual loss may occur in FS with fulminant intracranial hypertension that may necessitate urgent surgical intervention (e.g., external ventricular drain or ventriculoperitoneal shunt).
The prognosis of FS depends on the underlying etiology. Papilledema can produce permanent visual loss and fulminant cases with elevated ICP may require urgent or emergent surgical intervention.
FS is characterized by elevated CSF protein level, CSF xanthochromia, and hypercoagulability. Obstruction of CSF flow can occur from inflammatory, infectious, infiltrative, or neoplastic conditions. Ophthalmologists should be aware of FS and the common ophthalmic presentations of increased ICP (papilledema, non-localizing sixth nerve palsy). Fulminant cases may require urgent surgical intervention (like fulminant idiopathic intracranial hypertension (IIH)). Negative cranial imaging (e.g., MRI and MRV) may create a false sense of security and may mimic IIH. Spinal imaging is indicated for cases with elevated CSF protein or a “dry tap”.
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