How can I differentiate between primary and secondary Restless Legs Syndrome in my patients?

To differentiate between primary and secondary Restless Legs Syndrome (RLS) in patients, clinicians should first identify the presence or absence of underlying causes or associated conditions. Primary RLS is idiopathic, often familial, and typically presents without an identifiable precipitating factor, whereas secondary RLS is associated with other medical conditions or factors that may precipitate or exacerbate symptoms.

Key steps include:

• Clinical history and symptom assessment: Primary RLS usually manifests as an urge to move the legs accompanied by uncomfortable sensations, predominantly occurring at rest and worsening in the evening or night, without an obvious cause. Secondary RLS may present similarly but is linked temporally or causally to other conditions.
• Investigate for underlying causes: Check for iron deficiency anaemia or low serum ferritin (<50–75 micrograms/L), as iron deficiency is a common reversible cause of secondary RLS. Investigate and treat iron deficiency accordingly, even if anaemia is not overt ¹.
• Review medication history: Some drugs can precipitate or worsen RLS symptoms; identifying and modifying these can clarify secondary causes ¹.
• Consider associated conditions: Secondary RLS is often linked to pregnancy, chronic renal failure, peripheral neuropathy, or other neurological disorders. Pregnancy-related RLS typically resolves postpartum ¹.
• Laboratory and clinical evaluation: Beyond iron studies, assess for other systemic diseases or neurological disorders that may cause secondary RLS. The absence of such findings supports a diagnosis of primary RLS (Kumar et al., 2003; Hening et al., 2007).

In summary, primary RLS is a diagnosis of exclusion after ruling out secondary causes through clinical evaluation, laboratory tests (especially iron studies), and medication review. Referral to a specialist may be warranted if diagnosis is uncertain or treatment is unsuccessful ¹.