Hallucinogen Persisting Perception Disorder (HPPD)

• Among individuals who use hallucinogens, the prevalence is estimated to be approximately 4.2%.^[1]

• Little is known about the prognosis of HPPD.
• Depending on the individual, symptoms can last for weeks, months, or even years (rarely).^[2]
• Despite the perceptual disturbances, many individuals with HPPD can suppress the perceptual disturbances and continue to function normally.^[3]
• Up to 50% of cases may spontaneously remit on their own.^[4]

• Panic disorder, alcohol use disorder, and major depressive disorder are common comorbid mental disorders.^[5]

• The risk for HPPD appears to be highest with lysergic acid diethylamide (LSD) use, but not exclusively.^[6]
• There does not appear to be a correlation between the amount of hallucinogen use and HPPD, and thus the disorder appears to be a idiosyncratic phenomenon.^[7]

Following cessation of use of a hallucinogen, the reexperiencing of 1 or more of the perceptual symptoms that were experienced while intoxicated with the hallucinogen (e.g. - geometric hallucinations, false perceptions of movement in the peripheral visual fields, flashes of colour, intensified colours, trails of images of moving objects, positive afterimages, halos around objects, macropsia and micropsia).

The symptoms in Criterion A cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.

The symptoms are not attributable to another medical condition (e.g. - anatomical lesions and infections of the brain, visual epilepsies) and are not better explained by another mental disorder (e.g. - delirium, major neurocognitive disorder, schizophrenia) or hypnopompic hallucinations.

• The symptoms may include any perceptual perturbations, but visual disturbances tend to be predominant.
• A variety of perceptual disturbances have been reported, including images suspended in the path of a moving object, perceptions of entire objects, positive afterimages (i.e. , a same-coloured or complementary-coloured “shadow” of an object remaining after removal of the object), halos around objects, or misperception of images as too large (macropsia) or too small (micropsia).
• The perceptual disturbance may be episodic or continuous.
• A key part of making this diagnosis is that reality testing remains intact in HPPD (i.e. - the individual is aware that the disturbance is caused by the effect of the hallucinogen).

• The neural mechanisms behind HPPD remains poorly understood.
• It has been hypothesized that HPPD may be due to excitotoxic destruction of inhibitory interneurons that carry serotonergic and GABAergic receptors on their cell bodies and terminals.^[8]

• Intoxication and use of other drugs
  • Other substance intoxication and use disorders may also have symptoms similar to HPPD.
• Schizophrenia
  • In individuals with impaired reality testing, and other symptoms suggestive of psychosis may have an underlying primary psychotic disorder such as schizophrenia.
• Neurodegenerative disorders
  • Perceptual disturbances, along with cognitive changes may be early signs of an underlying neurodegenerative disorder.
• Medical conditions
  • Stroke, brain tumors, infections, and traumatic brain injuries may also cause similar perceptual disturbances.

• The results from neuroimaging in most cases of HPPD are typically negative with no acute findings. However, neuroimaging may still be warranted, depending on whether or not there are other neurological signs and symptoms, and the overall clinical presentation.^[9]

• A neurological exam may be warranted to rule out any other neurological causes.

• There are no approved treatments for HPPD.
• Most treatments are based on published case reports, and depends on the individual's clinical presentation.