An Interesting article:

Two or more conditions are comorbid when they occur at the same time within a patient. Comorbid conditions often interact with each other to aggravate the others’ symptoms yet remain independent of each other. Dissociative identity disorder (DID) is often comorbid with many different disorders because of the traumatic and highly stressful circumstances that cause it. Trauma, especially child abuse, is known to cause multiple averse effects later in life, and someone who is genetically predisposed to a disorder but might not necessarily have developed the disorder otherwise is more likely to have the disorder expressed if they survive trauma.

DID is most commonly comorbid with posttraumatic stress disorder (PTSD), a trauma- and stressor-related disorder that, like DID, is often the result of child abuse. In fact, DID and PTSD are so commonly comorbid that some have speculated that DID is actually an extreme version of PTSD. Others claim that DID and PTSD are so similar because both are possible outcomes of structural dissociation of the personality. Others claim that DID is more commonly associated not with PTSD but with complex-posttraumatic stress disorder (C-PTSD) due to the extreme and long term trauma that causes it.

Though reactive attachment disorder (RAD) is not diagnosed in adults nor necessarily associated with children with DID, it is worth nothing as another possible response to childhood trauma.

DID itself is the most extreme dissociative disorder and so includes features of all other dissociative disorders. These include dissociative amnesia, depersonalization/derealization disorder, and other specified dissociative disorder or unspecified dissociative disorder.

Somatic or conversion symptoms are also commonly present alongside DID. These involve physical symptoms that are not due to a physical disorder or a loss of functioning that would suggest the presence of a neurologic disorder that is not present. Somatic and conversion symptoms are classified as dissociative in nature. Of particular note are psychogenic non-epileptic seizures which are commonly seen in individuals with DID in other parts of the world.

Another disorder that is commonly comorbid with DID is borderline personality disorder (BPD). Like PTSD, BPD is commonly attributed to childhood trauma and disorganized attachment, though it is thought to have more of a genetic basis. BPD is also thought to result from structural dissociation. DID is sometimes accused of being the same condition as BPD, but there are many individuals with DID who do not fit the criteria for BPD.

Depressive and bipolar and related disorders, formerly known as mood disorders, are also commonly seen alongside DID as both can be triggered by trauma and high levels of stress. Major depressive disorder and persistent depressive disorder (dysthymia) are especially common as traumatized individuals fight to come to terms with what happened to them and how it affected them.

Like depressive and bipolar and related disorders, anxiety disorders are also often seen alongside DID due to being triggered by trauma and stress. Though PTSD triggers are separate from phobias, an individual with DID might have actual phobias due to having learned how quickly seemingly innocent situations and objects can turn harmful. Fear of punishment, judgment, or ridicule by parents can encourage social phobia, or social anxiety disorder. Generalized anxiety disorder is extremely common even in the general population, so it’s no surprise that individuals who have learned just how unsafe life can really be might be especially prone to it. Agoraphobia might take root similarly. Many alters in particular suffer from selective mutism due to threats made regarding what would happen to them if they ever spoke of the trauma that they survived.

Finally, though the presence of a feeding and eating disorder does not indicate abuse, feeding and eating disorders frequently follow abuse, trauma, or high levels of stress. Pica in particular is a sign of neglect, though both anorexia nervosa and bulimia nervosa can indicate an individual’s attempts to gain control over their life and body or shame over their body due to child abuse, particularly childhood sexual abuse.

DID can often been seen alongside obsessive-compulsive and related disorders, but as that combination is not quite as common, it is not discussed here.

Though DID can be comorbid with schizophrenia spectrum and other psychotic disorders, they are not especially likely to go together, so such disorders have not been detailed here. Dissociative psychosis is possible for individuals who have DID, and this can be diagnosed as brief psychotic disorder, but other conditions such as schizophrenia, delusional disorder, and schizoaffective disorder are not especially relevant to DID.

Other than BPD, DID is not especially likely to be accompanied by any personality disorders, though it would be most associated with cluster c personality disorders (avoidant, dependent, and obsessive-compulsive personality disorders). DID is not associated with paranoid, schizoid, or schizotypal personality disorders, and it is unknown how exactly comorbid DID and antisocial, histrionic, or narcissistic personality disorders would present if such combinations are possible. Antisocial and narcissistic personality disorders are discussed on this site only because of their high prevalence among perpetrators and so relevance to abuse survivors with DID.

DID can be comorbid with intellectual and neurodevelopmental disabilities and is especially common alongside autism spectrum disorders, but as intellectual and neurodevelopmental disabilities are neither caused nor triggered by trauma and the role that they may play in triggering DID is not yet understood, they are not discussed here.

Source: Comorbid and Related Conditions