Superficial siderosis - mechanism of disease: an alternative hypothesis.

Superficial siderosis is an increasingly common diagnosis due to advances in imaging. Resulting from the presence of blood in the subarachnoid space, it leads to progressively debilitating ataxia, deafness and myelopathy. Magnetic resonance imaging has revolutionized diagnosis and management of this condition. In one-third of patients with this diagnosis, no subarachnoid bleed can be identified. A lack of sensitivity in our ability to detect subarachnoid bleed is a possible explanation in this group of patients. A novel approach would be to consider defects in the body's defense against intracranial iron overload as a possible cause of this disease. A disproportionately few patients develop superficial siderosis compared with the number who develop subarachnoid bleed from various clinical conditions. Normal physiological protective mechanisms exist in the central nervous system to protect it from damage by blood, haeme or free iron. Deficiency and defect of these protective mechanisms can provide insight into the pathogenetic mechanism of the group of patients where no subarachnoid haemorrhage is identified.