There are several subtypes of delusional disorders and some of these include:

Persecutory delusion
This is the most common form of delusional disorder. In this form, the affected person fears they are being stalked, spied upon, obstructed, poisoned, conspired against or harassed by other individuals or an organization. As a result, the sufferer may retaliate violently against the persecution and/or turn to the law and other government agencies for support.

Delusion of grandeur
In this form of delusion, the person believes they are much greater or more influential than they really are. For example, they may be convinced they have an exceptional talent, extravagant riches or a special relationship with a prominent person.

Delusional jealousy
This usually develops due to a fear that a spouse or partner is being unfaithful. These doubts may be unfounded and can cause severe damage to the relationship. The sufferer usually goes to great lengths to try and find evidence of their partner’s alleged “affairs” and may also resort to a third party such as a private detective to find such evidence. Studies have shown that this form of delusion is more common in men than in women. It is sometimes called morbid jealousy or pathological jealousy.

Erotomania or delusion of love
In this form of delusion, the patient is often firmly convinced that a person he or she is fixated upon is in love with them. This obsession leads to stalking, unnatural jealousy and rage when the object of their affection is seen with their spouse or partners. Erotomanis often concern a famous person or someone who is in a superior status and usually there is no contact between the patient and the victim, who has never encouraged the patient. Erotomanic delusional disorder is also referred to as De Clerambault’s Syndrome.

Somatic delusional disorder
In this disorder, a person is convinced something is wrong with them. This type of delusion may often lead to multiple consultations with physicians, surgical procedures, depression and even suicide. Some individuals may also develop tactile hallucinations and feel the sensation of insects or parasites crawling over their skin. This is called monosymptomatic hypochondriacal psychosis and forms part of somatic delusional disorder.

Induced delusional disorder or folie a’ deux
This is a rare form of delusion where two people who are usually in a close relationship, are completely isolated from others physically and culturally and share the same delusional system of grandeur or persecution, for example. One of the partners may be the dominant personality who influences the weaker personality into adopting the delusion, in which case the psychosis mainly affects the dominant person, with the other rapidly recovering from the delusions once they are separated from them.

There are four categories of delusion and these include:

Bizarre delusion – Refers to delusion that is implausible or bizarre such as alien invasion

Non-bizarre delusion – Refers to delusion such as fear of being followed

Mood-congruent delusions – This is delusion that is consistent with the depressed or manic state of the sufferer. For example, when depressed, a person may feel delusions of persecution and when feeling manic, they may feel delusions of grandeur.

Mood-neutral delusions that are not influenced by mood.