Differential Diagnosis
The patient's symptoms of a rash in the eye, weakness of proximal muscles, and a history of 45 pack years of smoking suggest a complex underlying condition. Here's a categorized differential diagnosis:
Single Most Likely Diagnosis
- Dermatomyositis (paraneoplastic of lung CA): This condition is strongly suggested by the combination of skin rash, proximal muscle weakness, and a significant smoking history, which is a risk factor for lung cancer. Dermatomyositis can be a paraneoplastic syndrome associated with various cancers, including lung cancer.
Other Likely Diagnoses
- Polyarteritis: This is a systemic vasculitis that can present with a wide range of symptoms, including skin manifestations and muscle weakness. However, it is less directly linked to smoking and lung cancer compared to dermatomyositis.
- Scleroderma: While scleroderma can cause skin changes and potentially some muscle symptoms, it is less commonly associated with the specific combination of proximal muscle weakness and a significant smoking history.
Do Not Miss Diagnoses
- Lung Cancer with Metastasis: Given the patient's significant smoking history, it's crucial not to miss lung cancer, which could directly cause or be associated with the patient's symptoms, either through metastasis affecting muscles or through paraneoplastic syndromes.
- Vasculitis (e.g., Giant Cell Arteritis): Although less likely, vasculitis affecting the eyes and muscles could have serious consequences if not promptly treated.
Rare Diagnoses
- Inclusion Body Myositis: A rare inflammatory muscle disease that could cause progressive muscle weakness but is less likely to be associated with a rash or directly linked to smoking.
- Other Paraneoplastic Syndromes: There are various paraneoplastic syndromes associated with lung cancer that could present with neurological or muscular symptoms, though they are less common than dermatomyositis in this context.
Each of these diagnoses requires careful consideration of the patient's symptoms, history, and potentially additional diagnostic tests to determine the most accurate diagnosis and appropriate treatment plan.