1. What is the likely diagnosis?

• Hypoalbuminemia
• Secondary hypothyroidism much less likely. 

Note that there are no features specific for hypothyroidism although the sum total of signs and symptoms are superficially suggestive of this diagnosis.

2. What are the most likely causes?

• Nephrotic syndrome due to renal involvement from diabetes
• Nephrotic syndrome due to some other cause; 
• Cirrhosis due to hemochromatosis; 
• Secondary hypothyroidism

3. What additional aspects of the history and physical examination could provide relevant information to help in the diagnosis? 

• Symptoms related to diabetic control (poorer the control, more likely there is nephropathy)
• Presence of retinopathy (more likely in patient with nephropathy)
• Family history of hemochromatosis, history of darkening of skin
• Hepatomegaly
• Signs and symptoms related to a pituitary-hypothalamic mass
• Signs and symptoms of secondary hypoadrenalism
• Galactorrhea

4. What additional tests would help confirm the diagnosis? 

• 24 hour urine protein
• Serum albumin

5. What are the treatment options?

• Better diabetic control
• Better blood pressure control
• Low protein diet