tough question to exactly tell the differences. they are different with overlapping features.....
some material from some sites-----
A comparison of delusional and nondelusional body dysmorphic disorder in 100 cases. Phillips KA, McElroy SL, Keck PE Jr, Hudson JI, Pope HG Jr.
Personality Disorder and Psychosocial Research Program, McLean Hospital, Belmont, MA.
A controversial issue that was debated for DSM-IV is whether body dysmorphic disorder (BDD)--a preoccupation with an imagined defect in appearance--can be psychotic. BDD is classified separately from its delusional counterpart (delusional disorder, somatic type) in DSM-IV, but does it have a psychotic variant that overlaps with, and may even be the same diagnostic entity as, its delusional disorder variant? One hundred consecutive patients with DSM-III-R-defined BDD or its delusional variant were assessed with a semistructured interview, the Structured Clinical Inverview for DSM-III-R, and a modified version of the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). The 48 patients with nondelusional BDD were compared with the 52 patients with delusional BDD (i.e., delusional disorder, somatic type). The two groups did not differ significantly in terms of most variables examined, including demographics, phenomenology, course, associated features, comorbidity, and treatment response. Thus, BDD may have a psychotic subtype that significantly overlaps with, and may even be the same disorder as, its delusional disorder variant. However, delusional subjects had higher total scores on the modified Y-BOCS, suggesting that the delusional variant of BDD may be a more severe form of the disorder. Although preliminary, these findings have implications for BDD's treatment and classification, suggesting that inclusion of a delusional (psychotic) subtype of BDD should be considered for future editions of DSM.
there a table at emedicine.com---- d/d of delusional disorder----
Table 1. Differential Diagnoses
Disorder
Differentiating Factors
Substance-induced delusional disorders - Particularly stimulants, antihistamines, sympathomimetics, steroids, dopamine agonists, hallucinogens, and alcohol
Careful chronology of onset and persistence of delusional symptoms considering chronology of substance use
Mood disorders with delusions (manic and depressive types)
In mood disorders, mood symptoms and associated neurovegetative disturbances usually precede delusions, while in idiopathic delusional disorder, mood symptoms generally are mild, and delusional thought content may exist in the absence of mood symptoms.
Schizophrenia
Schizophrenia has positive and negative symptoms and greater functional impairment compared to relatively circumscribed delusions in delusional disorder.
Dementia and delirium
Mental status testing and chronological history demonstrate impairment of alertness in delirium and impairment of memory and other cognitive functions in dementia.
Elderly patients
Isolation, aging, medical problems and treatments, and sensory loss contribute to the increased incidence of delusions in elderly populations. This phenomenon is thought to be distinct from delusional disorder.
Body dysmorphic disorder
Significant overlap with delusional disorder and the 2 conditions often are diagnosed together. Few significant differentiating factors exist.
Obsessive-compulsive disorder
Significant overlap with delusional disorder and, if reality testing regarding obsessions or compulsions is lost, delusional disorder often is diagnosed.
Hypochondriasis
Hypochondriacal concerns generally are more amenable to reality testing and are less fixed than in delusional disorder.
Paranoid personality disorder
Does not include the presence of circumscribed delusions but, rather, a pervasive and stable pattern of suspiciousness or distrust.
Misidentification syndromes (includes Capgras syndrome)
These can be confused with delusional disorder. Increasing research is showing the prominence of CNS abnormalities in these conditions
Shared psychotic disorder
History regarding others with similar beliefs should be elicited.
Paraphrenia
Excluded from DSM (possibly because DSM allows hallucinations in delusional disorder); however, some maintain that it represents a separate diagnostic grouping. Paraphreniais defined by the presence of delusions and hallucinations in the absence of marked negative symptoms and personality deterioration. Delusional content is described as less organized, and hallucinations are more prominent than in paranoia (delusional disorder).
Other medical illnesses
Routine focused history, examination, and laboratory testing should screen for illnesses, including head injury, CNS infection, and epilepsy.
BDD tends to be chronic and can lead to social isolation, school dropout major depression, unnecessary surgery and even suicide.
It is often associated with social phobia and OCD, and delusional disorder. Chronic BDD can lead to major depressive disorder. If it is associated with delusions, it is reclassified as Delusional disorder, somatic subtype. Bromosis (excessive concerns about body odor) or Parasitosis (concern that one is infested by parasites) can classically be associated with delusions.
Other conditions that might be confused with BDD: Neglect caused by a parietal lobe brain lesion; anorexia nervosa, gender identity disorder.
Milder body image disturbances that do not meet criteria for BDD. :
Benign dissatisfaction with one’s looks. This does not affect the person’s quality of life. 30-40% of Americans may have these feelings.
Moderate disturbance with one’s body image. The person’s concerns about appearance cause some intermittent anxiety or depression.
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