Can major depressive disorder (MDD) with psychosis cause olfactory hallucinations?

Can Major Depressive Disorder with Psychosis Cause Olfactory Hallucinations?

Yes, major depressive disorder with psychosis can cause olfactory hallucinations, though they are uncommon and occur at lower rates than auditory or visual hallucinations.

Prevalence and Clinical Significance

• Olfactory hallucinations occur in approximately 20% of patients across primary psychotic disorders, including those with mood disorders with psychotic features 1
• While rarely emphasized in clinical descriptions, olfactory hallucinations are a recognized symptom of depressive disorder and should not be dismissed when present 2
• These hallucinations occur across all diagnostic categories of psychotic illness, with no single type of hallucinatory experience being pathognomonic to any specific diagnosis 1

Clinical Associations in Psychotic Depression

• When olfactory hallucinations occur in psychotic depression, they correlate with other hallucinations across sensory modalities and are associated with specific clinical features including:

  • Somatic delusions 1
  • Delusions of control 1
  • Thought broadcasting 1
  • Earlier age at onset of illness 1
  • Lifetime history of depressive episodes 1

• Olfactory hallucinations in depression have close relation to olfactory reference syndrome and may represent disturbed brain function in the depressive state 2

Diagnostic Implications

• The presence of delusions or hallucinations (including olfactory) in major depressive disorder indicates a severe form of that disorder 3
• Patients with psychotic depression have individually more severe depressive symptoms compared to those with nonpsychotic depression 3
• Secondary causes of psychosis must be ruled out, including central nervous system infections, neurologic causes such as dementia or traumatic brain injury, and substance-induced psychosis 4

Treatment Considerations

• Acute treatment of psychotic unipolar depression requires combination therapy with an antidepressant and an antipsychotic drug, or electroconvulsive therapy 5, 3
• Recovery is more rapid when antidepressants are combined with antipsychotics compared to monotherapy 3
• Electroconvulsive therapy is particularly effective for psychotic depression 3

Critical Pitfalls to Avoid

• Do not assume olfactory hallucinations automatically indicate a neurological disorder such as temporal lobe epilepsy, though this should be considered in the differential diagnosis 2
• Do not overlook that psychotic symptoms in depression may be fleeting or mild, not just severe and mood-congruent 5
• Do not miss secondary medical causes—legal medications and illicit substances (particularly cannabis and methamphetamine) can cause hallucinations that typically resolve within 30 days of abstinence 4