26th January 2024

Diagnosis

Depression is diagnosed using the Diagnostic and Statistical Manual of Mental Disorders 5ᵗʰ edition (DSM-5) or International Classification of Diseases 10ᵗʰ revision (ICD-10) criteria.

In order to make a diagnosis, patients must have at least 1 core symptom that has been present most of the time, on most days of the week, for at least 2 weeks.

There are various validated measures to assess patients presenting with depressive symptoms; these include:

• Patient Health Questionnaire-9 (PHQ-9) (https://www.mdcalc.com/calc/1725/phq-9-patient-health-questionnaire-9)
• Hamilton Depression Rating Scale (HAM-D) (https://www.mdcalc.com/calc/10043/hamilton-depression-rating-scale-ham-d)
• Major Depression Index (MDI) (https://www.mdcalc.com/calc/1844/major-depression-index-mdi)
• DSM-5 Criteria for Major Depressive Disorder (https://www.mdcalc.com/calc/10195/dsm-5-criteria-major-depressive-disorder)

Investigations are not routinely indicated but may be necessary to exclude other causes of depression or conditions that are known to be associated with depression. Any of these may co-exist with depression, and the presence of one does not exclude the possibility of another.

Investigations

• Blood glucose
  • Hyperglycaemia suggesting diabetes mellitus
• Urea, electrolytes & creatinine
  • Normal values suggesting electrolyte imbalances
  • Low eGFR, high creatinine suggesting renal dysfunction
• ESR & CPR
  • Raised suggesting infection or inflammation
• Liver function
  • LFTs suggestive of hepatic dysfunction
  • High GGT suggesting high alcohol intake
• Thyroid function
  • High T4 / low TSH indicating hyperthyroidism
  • Low T4 / high TSH indicating hypothyroidism
• Calcium Levels
  • Abnormal values indicative of hyper or  hypocalcaemia
• Full blood count
  • Low Hb indicating anaemia
• Urine drug screen
  • Suggesting substance use/misuse

Differential diagnosis

• Anxiety disorders
  • Can present with a wide range of physical and affective abnormalities, including fatigability, sleep disturbance, cognitive dysfunction, and unwanted thoughts.
  • These may present with physical symptoms not seen in depression, such as panic attacks, cognitive distortions, and muscle tension.
• Neurological conditions (such as Parkinson’s disease, Multiple Sclerosis, dementia)
  • Neurodegenerative and neurological diseases can be associated with affective symptoms, changes to behaviour and cognitive function, such as memory and attention. However, depression does not cause focal neurological signs, and the presence of these should alert to the possibility of other pathology.
• Substance misuse
  • Pharmacologic agents can have physiological effects on mood and behaviour
  • Substance abuse can often produce similar symptoms to depression, such as feelings of guilt or worthlessness, appetite changes, psychosis, and suicidal ideation
  • The substance use should pre-date the depressive symptoms in order to diagnose substance-induced depression
• Diabetes mellitus
  • Depression and diabetes share symptoms such as weight loss, fatigue, and low mood. However, the key difference is the blood glucose dysregulation defining diabetes.
• Chronic Obstructive Pulmonary Disorder
  • Physiological abnormalities such as hypoxaemia and hypercapnia can present with similar symptoms to depression, such as lethargy, impaired concentration, and irritability.
  • The presence of physiological changes in COPD, such as alterations to lung function, can help set the diagnoses apart.
• Hypothyroidism or hyperthyroidism
  • Endocrine disorders can produce changes similar to depressive disorders, such as lethargy, weight changes, and mood disturbance. However, endocrine diseases have distinct laboratory abnormalities to help identify them.
• Obstructive Sleep Apnoea Syndrome
  • Often produces feelings of fatigue, insomnia, cognitive deficits and decreased libido.
  • This is more common among patients with obesity and can be diagnosed using the aid of polysomnography.
• Infectious and inflammatory disorders
  • Many infectious and inflammatory disorders can produce neuropsychiatric signs and symptoms; however, they usually have other associated pathology that can be used to help identify them, such as sensory loss or biomarkers in the form of antibodies.

Always consider suicide and self-harm risk in patients with suspected depressive disorders.