Superficial siderosis is a Rare Disease: 

 is an exceptionally rare neurological disorder characterized by the deposition of hemosiderin,
an iron-storage complex, on the surface of the brain, spinal cord, and cranial nerves. This
condition arises due to chronic bleeding into the subarachnoid space, leading to progressive
neurological impairments(1).

The prevalence of superficial siderosis is estimated to be approximately 1 in 1,000,000 individuals.
As of 2024, there are an estimated 300 diagnosed cases in the United States(2)(3). This
rarity places superficial siderosis among the least common neurological disorders globally.
Due to its scarcity, superficial siderosis is not typically included in global rare disease rankings.
However, its estimated prevalence underscores its status as an exceptionally rare condition.  we hope to
change that by making known the disease to the Neurologists of the world(5).
It's important to note that the actual number of cases may be higher than reported, as the condition
is often misdiagnosed. This misdiagnoses is partly due to its nonspecific symptoms and the necessity of advanced imaging techniques, such as MRI, for accurate detection. 

In summary, while precise global rankings for rare diseases like superficial siderosis are not readily available, the condition's estimated prevalence of 1 in 1,000,000 highlights its exceptional rarity(6).  SS is a rare disease and it needs to be listed as such.  TSB will be exploring how we can make that so, we will update you in our June newsletter with regards to our progress.
 
REFERENCES:
Rare Diseases
1.AHA Journals
Prevalence and Natural History of Superficial Siderosis | Stroke
October 25, 2017 — Our findings indicate that cSS can be seen in ≈1% of people over age 70 in the general population. The subset of individuals with disseminated ...

2.Oxford Academic
Cortical superficial siderosis: detection and clinical significance in ...
June 25, 2015 — Cortical superficial siderosis (cSS) describes the deposition of blood-breakdown products over the cereSpringer Link

3.Springer Link
Prevalence of cortical superficial siderosis in patients with cognitive ...
November 13, 2013 — The prevalence of cSS in our sample of patients with cognitive impairment was 6.1 %, which is notably higher than the prevalence of cSS in the …

4.PubMed
Superficial siderosis in the general population - PubMed
July 21, 2009 — Results: We found that superficial siderosis was present in 7 (0.7%) individuals, all of whom had cerebral microbleeds in lobar locations.

5.American Academy of Neurology
Prevalence of cortical superficial siderosis in a memory clinic ...
The highest prevalence of 4.8% (95% CI 2.8%–8.2%) was observed in patients with AD. Among patients with “other dementia,” 2 patients had SS (2.5% [95% CI 0.7%– …

6.JNS Journal
Prevalence of infratentorial superficial siderosis in a large general ...
There are few studies describing the population prevalence of cerebellar or infratentorial siderosis, ranging between 0.03–0.14 %, none from the. UK population.