What is the Sneddons classification? Understanding a Rare Syndrome's Categorization

September 21, 2025 •

4 min read

First described in 1965, Sneddon's syndrome is a rare and complex neurocutaneous vasculopathy combining specific skin and neurological features.

So, what is the Sneddons classification? This article explains the two primary ways this syndrome is categorized, helping to clear up common misunderstandings.

Quick Summary

The Sneddons classification is not a single system but refers to two main ways of categorizing Sneddon's syndrome: by the presence of antiphospholipid antibodies (aPL-positive or aPL-negative) and by its etiology (primary or secondary).

Key Points

No Single System: The term "Sneddons classification" is misleading, as there are multiple ways to categorize Sneddon's syndrome, not one single, universally accepted classification system.
Two Primary Categories: The main classifications are based on antiphospholipid antibody status (aPL-positive or aPL-negative) and etiology (primary or secondary).
Livedo Racemosa is Key: The syndrome is characterized by livedo racemosa, a persistent, irregular skin mottling, not the more common, temporary livedo reticularis.
Neurological Impact: A key feature is recurrent cerebrovascular events like strokes and TIAs, which can lead to progressive cognitive decline over time.
Distinguish from Seddon's: It's important not to confuse Sneddon's syndrome with Seddon's classification, which categorizes nerve injuries, not vasculopathy.
Diagnosis is Clinical: Diagnosis relies on a combination of clinical presentation, lab tests for antibodies, and imaging, but there is no single definitive test.

Defining Sneddon's Syndrome

Sneddon's syndrome (SS) is a rare, non-inflammatory, chronic arteriopathy primarily characterized by the combination of two major clinical features: livedo racemosa and recurrent cerebrovascular events such as strokes and transient ischemic attacks (TIAs). The skin manifestation, livedo racemosa, is a persistent, reddish-blue, branching, and irregular net-like pattern that typically does not resolve with warming. Unlike the more common livedo reticularis, which is often temporary and can be physiological, livedo racemosa in SS is a pathological sign of underlying vascular obstruction. The neurological symptoms often appear years after the onset of the skin condition, making early diagnosis challenging.

Origins and Initial Identification

The syndrome was first described by British dermatologist Dr. Ian Bruce Sneddon in 1965, based on a series of patients with both a distinct skin rash and cerebrovascular lesions. The historical context is important because it highlights the ongoing debate in the medical community about whether Sneddon's syndrome represents a single disease entity or a collection of related disorders. This complexity is the very reason there isn't a single, universally accepted Sneddons classification, but rather a set of overlapping criteria.

The Antiphospholipid Antibody (aPL) Classification

One of the most frequently used classification systems for Sneddon's syndrome is based on the presence of antiphospholipid antibodies (aPL), which are autoantibodies that target components of the body's own cells and can promote blood clotting.

aPL-positive Sneddon's syndrome: In these cases, patients test positive for antiphospholipid antibodies. The aPL-positive group can be seen as an overlap with Antiphospholipid Syndrome (APS), a systemic autoimmune disease. Up to 80% of SS patients may test positive for these antibodies, although some studies report a lower prevalence. The presence of these antibodies suggests an immune-mediated mechanism for the vasculopathy.
aPL-negative Sneddon's syndrome: This group consists of patients who present with the classic livedo racemosa and cerebrovascular events but do not have detectable antiphospholipid antibodies. The pathogenesis in this subgroup is less understood, and ongoing research is exploring other potential etiologies, including genetic predispositions and inflammatory pathways.

Clinical and Prognostic Differences

While both aPL-positive and aPL-negative patients experience the characteristic symptoms of SS, there can be subtle clinical differences and variations in disease course. For example, aPL-positive patients might have a higher risk of recurrent thrombosis, while aPL-negative patients may have distinct underlying pathogenic mechanisms.

Primary vs. Secondary Classification

Another classification system divides Sneddon's syndrome based on its etiology, or underlying cause. This approach was notably proposed by Schellong et al. in 1997.

Primary Sneddon's syndrome: This category applies to patients where no obvious underlying cause or associated systemic disease can be identified. It is considered idiopathic and is a diagnosis of exclusion.
Secondary Sneddon's syndrome: This designation is used when SS occurs in the presence of another identifiable autoimmune or thrombophilic disorder. Common associations include systemic lupus erythematosus (SLE) and other connective tissue diseases. The secondary form is often treated by managing the underlying condition.

Sneddon's Classification vs. Seddon's Classification

It is crucial to distinguish Sneddons classification from the unrelated Seddon's classification of nerve injuries. Named after Sir Herbert Seddon, this system categorizes peripheral nerve damage into three types: neurapraxia, axonotmesis, and neurotmesis. The similar-sounding names can cause confusion, but the topics are entirely different, relating to vasculopathy and nerve damage, respectively.

Comparison of Livedo Types

This table highlights the key differences between livedo reticularis and livedo racemosa, which is central to the diagnosis of Sneddon's syndrome.


Feature	Livedo Reticularis (LR)	Livedo Racemosa (LRC)
Appearance	Fine, regular, net-like pattern with complete circles	Broken, irregular, branching net-like pattern with incomplete circles
Persistence	Often temporary, may resolve with warming	Persistent and permanent, does not resolve with warming
Associated Condition	Can be physiological (cutis marmorata) or primary	Almost always pathological; a hallmark of Sneddon's syndrome
Cause	Sluggish venous blood flow or small capillary constriction	Persistent obstruction of peripheral arterial blood flow

Diagnostic Approach and Challenges

The diagnosis of Sneddon's syndrome is primarily clinical, based on the combination of livedo racemosa and recurrent strokes. However, given the variability and overlap with other conditions like APS, a comprehensive workup is essential. This typically involves:

Clinical Evaluation: A detailed history and physical examination, noting the characteristics of the skin rash and any neurological symptoms.
Laboratory Tests: Screening for antiphospholipid antibodies (anticardiolipin, lupus anticoagulant, and anti-beta 2-glycoprotein I) to determine aPL status. Other tests may include markers for systemic inflammation and autoimmune disease.
Imaging Studies: A brain MRI is often performed to identify ischemic strokes, white matter lesions, and cerebral atrophy, which are common findings in SS.
Skin Biopsy: A deep skin biopsy may reveal the characteristic non-inflammatory thrombotic vasculopathy of the small to medium-sized dermal arteries.

The diagnostic process is further complicated by the fact that the skin rash can precede neurological symptoms by many years, and the syndrome can mimic other conditions. Early and accurate diagnosis is critical for appropriate management, which typically involves antithrombotic agents to reduce the risk of future strokes. For more comprehensive details on the syndrome itself, consult reliable resources like the National Organization for Rare Disorders (NORD).

Conclusion: Navigating a Complex Syndrome

In conclusion, there is no single Sneddons classification but rather several classification schemes that help categorize patients with this rare syndrome. The primary methods are based on antiphospholipid antibody status (aPL-positive or aPL-negative) and etiology (primary or secondary). These classification systems are crucial for understanding the potential underlying mechanisms of the disease and guiding management strategies. Given its rarity and complex presentation, it is essential for healthcare professionals to be aware of these diagnostic nuances to ensure timely and accurate diagnosis for affected individuals.

Frequently Asked Questions

Sneddon's syndrome is primarily diagnosed based on the clinical presentation of livedo racemosa and recurrent cerebrovascular events, confirmed with brain MRI and laboratory tests for antiphospholipid antibodies. A deep skin biopsy can also reveal characteristic vascular changes.

Livedo racemosa, a key feature of Sneddon's syndrome, is a persistent, irregular, branching skin discoloration that indicates underlying vascular pathology. Livedo reticularis, in contrast, is a finer, more regular pattern that can be a temporary, physiological response to cold.

If a patient's Sneddon's syndrome is aPL-positive, it means they have detectable levels of antiphospholipid antibodies in their blood. This suggests an overlap with Antiphospholipid Syndrome (APS) and indicates a potential immune-mediated mechanism behind the thrombotic events.

Yes, Sneddon's syndrome can be classified as 'primary' when there is no obvious associated autoimmune disorder or thrombophilic state. This is a diagnosis of exclusion after a thorough evaluation.

Management for Sneddon's syndrome is primarily focused on stroke prevention using antiplatelet or antithrombotic medications, such as warfarin. There are no controlled studies to guide therapy, so treatment is often based on individual needs and anecdotal evidence.

Sneddon's syndrome is a progressive condition. The cumulative effect of recurrent ischemic strokes can lead to cognitive decline, memory loss, early-onset dementia, and other significant neurological deficits over time.

While most cases of Sneddon's syndrome are sporadic, some familial cases have been reported, suggesting a potential autosomal dominant inheritance pattern in some instances. However, the majority of cases are not inherited.