Chronic pain and depression. IV. DST as a discriminator between chronic pain and depression

In an attempt to clarify the relationship between chronic pain and depression, the authors studied the plasma cortisol response to dexamethasone in a group of 73 consecutive chronic low back pain patients admitted to a pain unit and 34 consecutive patients admitted to an affective disorders unit with the principal diagnosis of primary major depression. Patients with chronic pain were evaluated as to the presence or absence of major depression and patients with primary major depression were evaluated as to the presence or absence of pain complaints as part of their presenting symptomatology. Chronic pain patients with major depression differed significantly from chronic pain patients without major depression (3.4 +/- 3.33 micrograms/dl versus 1.6 +/- 0.9 micrograms/dl, P less than 0.05). Chronic pain patients with major depression also differed from patients with primary major depression with pain complaints (3.4 +/- 3.3 micrograms/dl versus 10.7 +/- 8 micrograms/dl, P less than 0.0005). The values given are post-dexamethasone plasma cortisol levels. Patients having primary major depression with pain complaints do not significantly differ from patients having primary major depression without pain complaints. The dexamethasone suppression test may be a useful method in discriminating those patients with chronic pain versus those with primary major depression, chronic pain patients with major depression versus those with primary major depression and chronic pain patients with major depression versus those with chronic pain and no depression.