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Differential Diagnosis: Obsessive-Compulsive Disorder vs. Illness Anxiety Disorder vs. Somatic Symptom Disorder

By April 21, 2020April 6th, 2021Andrew Cohen, M.S., Blogs

How does one go about correctly diagnosing a patient who presents with preoccupations about their health?   There are many different diagnoses that these symptoms could fall under, including a physical medical condition, Obsessive-Compulsive Disorder, Illness Anxiety Disorder, and Somatic Symptom Disorder.  This article will address what each of these disorders looks like and how to differentiate them. Additionally, discussion about treatment for these disorders will be addressed.

Before going into each psychological disorder, it is essential to note that a full physical by a medical professional should be conducted to rule-out physical medical conditions that are causing the patient’s symptoms.

Obsessive-Compulsive Disorder

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) defines Obsessive-Compulsive Disorder (OCD) as follows:


  1. Recurrent and persistent thoughts, urges or images (obsessions) that are experienced, at some time during the disturbance, as intrusive, unwanted, and that in most individuals cause marked anxiety or distress.
  2. The individual attempts to ignore or suppress such thoughts, urges, or images, or to neutralize them with some thought or action (i.e., by performing a compulsion).


  1. Repetitive behaviors (e.g., hand washing, ordering checking) or mental acts (e.g., praying, counting, repeating words silently) that the person feels driven to perform in response to an obsession, or according to the rules that must be applied rigidly.
  2. The behaviors or mental acts are aimed at preventing or reducing distress or preventing some dreaded event or situation. However, these behaviors or mental acts either are not connected in a realistic way with what they are designed to neutralize or prevent or are clearly excessive.

A Person diagnosed with OCD may experience obsessions that are related to their health and well being such as, “What if touching that doorknob gives me some illness?” “What if that red spot on the floor is blood, and if I go near it I will contract HIV?” “What if I come into contact with someone who is sick, and I get their illness?” A person experiencing these obsessions may engage it compulsions such as excessive washing of their hands, avoiding touching certain surfaces, avoiding anything that resembles blood, or avoiding populations of people who are more prone to having certain diseases.

Illness Anxiety Disorder

The DSM-5 defines Illness Anxiety Disorder as follows:

  • Excessive worry about having or developing a debilitating or life-threatening illness.
  • Somatic symptoms are absent. If somatic symptoms are present, they are only mildly distressing to the patient. If a medical condition is present or a high-risk for developing a medical condition is present (due to family history), the anxiety regarding the medical condition (or potential impending medical condition) is excessive.
  • Excessive concern and anxiety regarding health-related issues.
  • The individual exhibits disproportionate and redundant health-related behaviors, such as repeatedly checking his or her body for indications of disease.
  • Symptoms have been present for at least 6 months
  • The illness-related preoccupation is not better explained by another psychiatric condition

A person experiencing illness anxiety disorder will present with symptoms such as excessive worry about having or getting a particular illness (i.e., cancer, hepatitis, HIV, Alzheimer’s, Dementia).  In response to these fears, the patient will engage in certain behaviors to make sure the fears do not come true.  People with Illness Anxiety Disorder will fall under two categories:

  1. Care-seeking type
  2. Care-avoidant type.

A person with care-seeking type will continuously go to different doctors or the same doctor over again seeking reassurance they are okay.  Even though this person has been told numerous times they do not have whatever illness they are worried about, they continuously doubt the results and want to keep going back for more tests.

A person with care-avoidant type will actively avoid going to doctors and medical offices, as they are worried that if they go, the person will be told they have the illness they are scared of.  A person with care-avoidant type may go years between doctor’s visits and can actually be more prone to developing a physical illness due to this.

Somatic Symptom Disorder

The DSM-5 defines Somatic Symptom Disorder as follows:

  • One or more somatic symptoms that are distressing or result in significant disruption of daily life.
  • Excessive thoughts, feelings, or behaviors related to the somatic symptoms or associated health concerns as manifested by at least one of the following:
  • Disproportionate and persistent thoughts about the seriousness of one’s symptoms.
  • Persistently high level of anxiety about health or symptoms.
  • Excessive time and energy devoted to these symptoms or health concerns.
  • Although any one somatic symptom may not be continuously present, the state of being symptomatic is persistent (typically more than 6 months).

A person experiencing somatic symptom disorder is typically hypersensitive to normal bodily functions and interprets them as some severe problem they are experiencing. A person with this disorder may interpret their stomach rumbling as a sign of a serious infection or disease rather than them just being hungry or gassy.  Additionally, people with this disorder will frequently visit doctors and other medical professionals often complaining of the same physical symptoms, and regular medical interventions do not alleviate the physical symptoms.  For example, someone experiencing constant nausea, and has somatic symptom disorder, may not respond to the medication that is administered to treat nausea.  A person with somatic symptom disorder will spend an excessive amount of time thinking and interpreting what the physical sensations may be and may engage in behaviors such as searching symptoms on the internet and seeking reassurance from medical professionals, family, and friends.

Differential Diagnosis

How do we decide the right diagnosis for patients, as a lot of symptoms and behaviors associated with these disorders are similar?

Patients presenting with OCD will exhibit several different symptoms than someone with Illness Anxiety Disorder or Somatic Symptom Disorder.  A person with OCD may experience health obsessions (i.e., getting contaminated, getting HIV, getting cancer) as well as somatic obsessions (i.e., constant worry about physical sensations).  However, this person will likely experience other categories of obsessions as well. These may include but are not limited to harm obsessions (i.e., fear of harming others or getting harmed by others); ordering and arranging obsessions (obsessions with evenness and the arrangement of things); or sexual obsessions (i.e., questioning sexual orientation, questioning one’s gender, or fears of being a pedophile).  There are many other categories of obsessions that can occur as well.

Additionally, a person with OCD may engage in more ritualistic behaviors to alleviate themselves from the distress associated with thoughts of becoming ill. These behaviors may include repeatedly praying, neutralizing bad thoughts, actively avoiding touching certain surfaces, excessive Internet searches, and excessive hand washing and cleaning compulsions.  In differentiating between OCD versus the other two disorders, it is crucial to determine if there are more areas of excess worry and concern in addition to the patient’s preoccupations with illness and somatic symptoms.  Additionally, patients with OCD engage in more ritualistic behaviors rather than just frequent doctor visits or avoiding medical professionals like in Illness Anxiety Disorder and Somatic Symptom Disorder

Patients presenting with Illness Anxiety versus OCD or Somatic Symptom Disorder typically only fear to contract a specific illness (i.e., Cancer, Alzheimer’s, Dementia).  This person usually will not be experiencing excessive worry surrounding other areas of concern, like a person experiencing OCD would.  A person with illness anxiety will also not be engaging in as many ritualistic behaviors as you would see with a patient with OCD.  Sometimes, patients with Illness Anxiety Disorder will experience somatic symptoms.  The difference between this and Somatic Symptom Disorder is that in Illness Anxiety, the bodily symptoms are not primary concern, and they are more concerned with the possible illness that is indicated by said somatic symptoms rather than the somatic symptoms themselves.

Patients presenting with Somatic Symptom Disorder will look different than the other two disorders as the main fears surround the actual physical sensations they are experiencing and the misinterpretations of said sensations versus the actual illness itself or other obsessive worries.  This person may be concerned with a specific illness; however, their main focus will be on the physical sensation (i.e., nausea, shortness of breath) rather than the illness or condition itself (i.e., Flu or COVID-19).  Additionally, this person will not be experiencing other unrelated fears and rituals, as discussed above, with OCD.


The good news is, no matter what the above disorder your patient is diagnosed with, treatment is relatively similar.  These disorders are all treated with Cognitive Behavioral Therapy (CBT), more specifically, Exposure and Response Prevention (ERP).  Through ERP, the patient is gradually exposed to their fears (i.e., being contaminated, being diagnosed with cancer, or increased heart rate or any physical sensation).  The patient then reframes from engaging in any behaviors to obtain quick relief  (i.e., washing hands, seeking reassurance from the internet, or going to the doctor).  This process helps retrain the patient’s fight or flight response to show that they are not actually in danger and ultimately helps the patient build their distress tolerance muscle to tolerate uncertainty.  The ultimate goal of ERP is to accept and tolerate uncertainty.  With any of the above disorders, we want the patient to be able to accept the possibility and uncertainty and understand that though the probability is low, they may become contaminated. They may actually have their feared illness, or that physical sensation they are experiencing may mean something serious.  Despite these odds, the patient can learn to live their life without the interference of these intrusive thoughts consuming them while engaging in senseless behaviors to obtain temporary relief and a false sense of certainty.

If you feel you or a loved one may be suffering from any of the disorders discussed in this article or any other anxiety disorder, please do not hesitate to reach out for a free 30-minute phone consultation to discuss treatment options.  Please call our Clinical Coordinator at 310-268-1888.