Atypical

In a psychological diagnosis "atypical" refers to symptoms that are recognized as part of mental illnesses yet do not rise to the level needed for diagnosis as part of recognized syndromes or do not respond to outside stimuli in the manner most common to a syndrome.

To be labeled atypical does not designate that the symptoms being seen are uncommon or rare, mainly that they do not conform to formally recognized conditions or syndromes.

For instance, atypical depression presents with the normal depressive symptoms such as sadness, lack of energy, and a lack of interest in normally pleasurable activities. Atypical depression is likely to also present with increased appetite/significant weight gain, hypersomnia, heaviness in the limbs as well as a tendency to react positively to good news or happy occasions.