Differential Diagnosis
The patient presents with generalized fatigue, myalgia, cramps, significantly elevated TSH (90), low T4 (0.2), elevated CK, and generalized swelling. Here's a categorized differential diagnosis:
Single Most Likely Diagnosis
- Hypothyroidism: The elevated TSH and low T4 levels are indicative of primary hypothyroidism. The symptoms of fatigue, myalgia, and generalized swelling are classic for hypothyroidism. Elevated CK can also be seen due to muscle involvement.
Other Likely Diagnoses
- Rhabdomyolysis: Although less likely than hypothyroidism given the thyroid function tests, rhabdomyolysis could explain the elevated CK and myalgia. However, it would not directly account for the thyroid hormone abnormalities.
- Polymyositis/Dermatomyositis: These inflammatory myopathies could cause muscle weakness, myalgia, and elevated CK. While they might not directly cause thyroid dysfunction, they can be associated with other autoimmune diseases, including autoimmune thyroiditis (e.g., Hashimoto's thyroiditis, which could lead to hypothyroidism).
Do Not Miss Diagnoses
- Thyroid Storm (in the context of untreated or undertreated hyperthyroidism leading to a thyrotoxic crisis, though the labs provided suggest hypothyroidism): Although the patient's labs suggest hypothyroidism, it's crucial to consider the possibility of thyrotoxic crisis in any patient with severe symptoms that could be related to thyroid dysfunction, as it is life-threatening.
- Adrenal Insufficiency: This condition can present with fatigue, myalgia, and could potentially have some overlap in laboratory findings or clinical presentation, especially if there's concomitant adrenal and thyroid dysfunction (e.g., Schmidt's syndrome).
Rare Diagnoses
- Glycogen Storage Diseases: Certain types of glycogen storage diseases can lead to muscle cramps, weakness, and elevated CK levels. However, they would not directly explain the thyroid function abnormalities.
- Mitochondrial Myopathies: These are a group of disorders that affect the mitochondria, leading to muscle weakness and could potentially cause elevated CK. They are rare and might not directly relate to the thyroid hormone abnormalities but could be considered in a differential diagnosis for myopathic symptoms.