What could be responsible for the 4.5kg weight gain and increased hunger in a 30-year-old female patient with Polycystic Ovary Syndrome (PCOS) and mental health issues, taking lithium, venlafaxine, pregabalin, metformin (1g), and melatonin, with recent changes in medication dosages, including an increase in lithium from 600mg to 800mg, insertion of a Mirena (levonorgestrel) intrauterine device, and addition of an estrogen patch (initially 50mcg, then reduced to 25mcg and 12.5mcg)?

Differential Diagnosis

The patient's symptoms of weight gain and increased hunger can be attributed to various factors. Here's a categorized differential diagnosis:

• Single most likely diagnosis
  • Lithium increase: The recent increase in lithium dosage from 600mg to 800mg in March could be contributing to the patient's weight gain and increased hunger. Lithium is known to cause weight gain as a side effect, especially when the dosage is increased.
• Other Likely diagnoses
  • Estrogen patch: The introduction of the estrogen patch in April, although the dosage has been tapered, could be contributing to the weight gain. Estrogen therapy can lead to increased appetite and weight gain.
  • Pregabalin increase: The increase in pregabalin dosage from 150mg to 225mg in late March may also be a contributing factor. Pregabalin is known to cause weight gain as a side effect.
  • Mirena coil: The insertion of the Mirena coil in March could be causing hormonal changes, leading to increased hunger and weight gain.
  • Metformin reduction in efficacy: Although the patient is on metformin for PCOS, the recent weight gain could indicate a reduction in the medication's efficacy, leading to increased insulin resistance and hunger.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Hypothyroidism: Although not directly related to the recent medication changes, hypothyroidism is a common condition in patients with PCOS and can cause weight gain and increased hunger. It's essential to rule out hypothyroidism, as untreated hypothyroidism can have severe consequences.
  • Cushing's syndrome: This rare endocrine disorder can cause weight gain, increased hunger, and other symptoms. Although unlikely, it's crucial to consider Cushing's syndrome, as it can be life-threatening if left untreated.
• Rare diagnoses
  • Insulinoma: A rare pancreatic tumor that produces excess insulin, leading to weight gain and increased hunger.
  • Growth hormone-secreting tumor: A rare pituitary tumor that can cause weight gain, increased hunger, and other symptoms.
  • Other rare endocrine disorders: Such as leptin deficiency or leptin receptor deficiency, which can cause severe obesity and hyperphagia.