Superficial siderosis is a rare neurological disorder caused by the accumulation of an iron-based compound, hemosiderin, on the surfaces of the brain and spinal cord. The condition results from chronic, slow bleeding into the subarachnoid space, the area filled with protective cerebrospinal fluid. Over years, red blood cells in this fluid break down, releasing iron that deposits onto the central nervous system. This progressive buildup is toxic to nerve cells and leads to a gradual decline in neurological function.
Underlying Causes of Bleeding
The chronic bleeding that causes superficial siderosis can originate from several sources. Many cases are linked to prior physical trauma to the head or spine that created fragile blood vessels. Complications from past brain or spinal surgeries are another common origin, where dural defects or tears result in a slow bleed. Other identified causes include tumors within the central nervous system, vascular malformations, or aneurysms that leak intermittently.
Despite thorough investigation, the specific site of bleeding cannot be located in around 35% of cases. This is referred to as idiopathic superficial siderosis. In these instances, the bleeding is presumed to be too slow or from a location that is difficult for current medical technology to pinpoint.
Neurological Signs and Symptoms
The neurological impact of superficial siderosis is progressive, with symptoms developing over many years as iron deposition damages nerve tissue. There can be a delay of 10 to 30 years between the initial bleed and the onset of symptoms. The condition is recognized by a classic triad of symptoms, though presentation varies depending on where iron accumulation is most severe.
The most common and earliest symptom is progressive sensorineural hearing loss. This hearing impairment is typically bilateral and results from hemosiderin damaging the eighth cranial nerve, which is responsible for hearing and balance. The nerve’s long course through the subarachnoid space makes it particularly vulnerable.
A second component of the triad is ataxia, which involves problems with balance and coordination. Patients often develop an unsteady, wide-based gait and may struggle with fine motor tasks. This results from damage to the cerebellum, a part of the brain that governs motor control.
The third symptom is myelopathy, or dysfunction of the spinal cord. This can manifest as muscle stiffness and spasticity in the legs, weakness, and altered sensations. Beyond this triad, individuals might also experience cognitive changes, headaches, or a diminished sense of smell (anosmia).
The Diagnostic Process
Confirming a diagnosis of superficial siderosis relies on advanced medical imaging. The most effective diagnostic tool is Magnetic Resonance Imaging (MRI). Specific MRI sequences, like Gradient Echo (GRE) and Susceptibility-Weighted Imaging (SWI), are highly sensitive to iron. On these scans, the deposits appear as a characteristic dark, linear rim coating the surface of the brain and spinal cord, which is a definitive sign of the condition.
In addition to imaging, a lumbar puncture (spinal tap) may be performed to analyze the cerebrospinal fluid. The presence of red blood cells or xanthochromia (a yellowish discoloration indicating old blood) can provide evidence of a bleed. Elevated levels of iron or the protein ferritin in the fluid can further support the diagnosis.
Approaches to Treatment
The management of superficial siderosis focuses on stopping the source of the bleeding and addressing existing iron deposits. The first goal is to identify and repair the site of the chronic hemorrhage to prevent further accumulation. If a cause like a dural tear or tumor is found, neurosurgical or endovascular procedures may be used to correct it.
The second objective is to manage the accumulated iron using chelation therapy, with the drug deferiprone being the primary agent. Deferiprone can cross the blood-brain barrier, bind to the excess iron, and help remove it from the body. This therapy aims to slow or stop the advancement of neurological symptoms by reducing the toxic iron load.
While chelation therapy can reduce iron deposits visible on an MRI, reversing existing neurological damage is a challenge. Clinical improvement is not guaranteed and can take months or years to become apparent. The effectiveness of deferiprone is an area of active research, but it remains a primary therapeutic option.