Aetiology

Primary insomnia accounts for 15% of cases. There is a great variation in the amount of sleep that is required by different individuals and it is likely that many people with primary insomnia are having enough sleep without realising it. It can be divided into:

• idipathic insomnia - a persistent disease which begins during infancy or childhood
• psychophysiologic insomnia - caused by heightened arousal and learned sleep-preventing associations
• paradoxical insomnia - patient complains of severe insomnia without any objective evidence of sleep disturbance (1)

Causes of secondary insomnia (comorbid insomnia) include:

• psychosocial stressors
  • situational stress - occupational, interpersonal, financial, academic, medical
  • environmental stressors - noise
  • death or illness of a loved one (2)
• psychiatric disorders
  • mood disorders: depression, bipolar disorder, dysthymia
  • anxiety disorders: generalized anxiety disorder, panic disorder, post-traumatic stress disorder
  • psychotic disorders: paranoia, schizophrenia, delusional disorder
• medical disorders
  • cardiovascular - angina, congestive heart failure
  • respiratory - chronic obstructive pulmonary disease, asthma
  • neurological - Alzheimer disease, Parkinson disease, head injury
  • rheumatological - fibromyalgia, chronic fatigue syndrome, osteoarthritis
  • gastrointestinal - gastroesophageal reflux disease, irritable bowel syndrome
  • sleep disorders - restless legs syndrome, sleep apnoea, circadian rhythm disorders
• drug and substance abuse
  • excessive use of alcohol or alcohol
    • after stopping heavy drinking sleep may be disturbed for several weeks
  • tobacco
  • recreational drugs
• medications
  • antihypertensives - beta-blockers
  • lipid lowering - statins
  • antidepressants - selective serotonin reuptake inhibitors, venlafaxine, bupropion, duloxetine, monoamine oxidase
  • hormones - oral contraceptive pills, cortisone, thyroid supplement
  • sympathomimetics - albuterol, salmeterol, theophylline, pseudoephedrine (1)

Reference:

• 1. Budur K et al. Advances in treating insomia. Cleveland Clinic Journal of Medicine 2007;74(4):251-266
• 2. Ramakrishnan, K. and Scheid, D.C. Treatment options for insomnia. American Family Physician 2007;76(4):5-526