SAT-203 Misleading Diagnosis of Cushing’s Syndrome on Pramipexole

We present an intriguing case of a patient incorrectly diagnosed with Cushing’s disease secondary to pramipexole use for restless leg syndrome (RLS). 61-year-old male with symptoms of 55 lb weight gain, progressive fatigue, and subjective muscle weakness presented to endocrinology office for work-up of possible Cushing’s syndrome. Physical exam was significant for mild facial plethora, purple striae, and central obesity. Patient’s history includes diagnosis of prolactin-producing pituitary microadenoma 30 years ago treated with bromocriptine with normalization of prolactin and resolution of adenoma. Patient notes ten years ago, he was started on pramipexole 1 mg TID for severe RLS. Given patient’s clinical symptoms he underwent hormonal testing which was notable for an abnormal 1 mg ONDST with morning cortisol 2.44 mcg/dL (normal &lt 1.8 mg/dL) and two abnormal late night salivary cortisol 0.177 mcg/dL and 0.199 mcg/dL (normal &lt 0.122). Repeat MRI showed a 0.4 cm hypoenhancing lesion in the left side of the anterior pituitary gland. Patient was referred for IPSS. His central-to-peripheral plasma ACTH ratio was as follows: before CRH administration: left 5.8, right 1.2; after CRH administration: left 16.4, right 2.7. These results demonstrated positive IPSS indicating centralization or a pituitary source of ACTH excess. Patient was going to be referred to neurosurgery for left pituitary adenoma resection, but literature search revealed a study showing pramipexole causing an increase in cortisol levels in physiologic studies involving healthy subjects. Due to these findings, labs were repeated while holding pramipexole. His morning cortisol and ACTH levels were normal. Late night salivary cortisol x3 were normal: 0.038, 0.071, and 0.024 mcg/dL (normal &lt 0.090 mcg/dL). The 24 hour urine free cortisol x2 was also normal. These negative biochemical findings showed no evidence of hypercortisolism off of pramipexole. This further complicated the case as the patient had positive IPSS. In order to help exclude the diagnosis of an ACTH secreting pituitary tumor, a DDAVP stimulation test was performed showing a normal response. Based on these tests it was concluded he does not have Cushing’s and that his hypercortisolism was related to pramipexole use. Repeat brain MRI showed no structural evidence of any pituitary lesion. We report a very rare case of pramipexole use leading to a false diagnosis of Cushing’s syndrome. This was fortunately identified prior to patient undergoing unnecessary surgery. We recommend awareness of pramipexole use associated with hypercortisolism to prevent incorrect diagnosis of Cushing’s syndrome. Schilling, J. C., Adamus, W. S., & Palluk, R. (1992). Neuroendocrine and side effect profile of pramipexole, a new dopamine receptor agonist, in humans. Clinical Pharmacology & Therapeutics, 51(5), 541-548.