How can I differentiate between primary insomnia and insomnia secondary to other medical or psychiatric conditions?

Differentiating primary insomnia from insomnia secondary to other medical or psychiatric conditions involves a thorough clinical assessment focusing on the onset, context, and associated features of the sleep disturbance.

Primary insomnia is characterised by difficulty initiating or maintaining sleep without an identifiable underlying medical, psychiatric, or environmental cause. It often presents as a chronic condition with no clear precipitating factor and is typically diagnosed after excluding other causes. In contrast, secondary insomnia occurs as a symptom or consequence of another condition such as anxiety, depression, chronic pain, neurological disorders, or medication effects.

Key steps to differentiate include:

• Comprehensive history and clinical assessment: Evaluate the temporal relationship between insomnia and other medical or psychiatric symptoms. If insomnia precedes or occurs independently of other conditions, primary insomnia is more likely. Conversely, if insomnia develops concurrently with or following another illness or psychological disorder, secondary insomnia should be suspected ¹.
• Screen for comorbidities: Assess for anxiety, depression, chronic pain, neurological disorders (e.g., obstructive sleep apnoea, restless legs syndrome), and medication side effects, as these commonly cause secondary insomnia ¹.
• Consider sleep disorder symptoms: Presence of symptoms such as loud snoring, apnoeas, parasomnias, or excessive daytime sleepiness may indicate another sleep disorder rather than primary insomnia, warranting specialist referral ¹.
• Use of sleep diaries and questionnaires: These tools help characterise sleep patterns and identify triggers or maintaining factors, aiding differentiation ¹.
• Evaluate psychosocial stressors and environmental factors: Stress, poor sleep hygiene, and lifestyle factors can contribute to both primary and secondary insomnia but are particularly relevant in primary insomnia ¹.
• Consider psychiatric evaluation: Since insomnia is often comorbid with psychiatric disorders, a mental health assessment is essential to identify secondary causes ¹.

Recent literature emphasises that insomnia is frequently multifactorial, and strict separation into primary versus secondary categories may be less clear-cut. Insomnia can be both a symptom and a perpetuating factor in psychiatric and medical disorders, necessitating a holistic approach to diagnosis and management (Gupta et al., 2014; Becker, 2006).

Summary: Differentiation relies on excluding other causes through history, examination, and targeted investigations, recognising comorbidities, and considering the temporal relationship of insomnia to other conditions. When doubt exists, or if treatment fails, referral to a sleep specialist is advised ¹.