Differential Diagnosis for Polyarthralgias, Rash, Hair Loss, Weight Gain, and Fatigue

Single Most Likely Diagnosis

• Hypothyroidism: This condition is characterized by fatigue, weight gain, hair loss, and sometimes polyarthralgias and rash (due to associated autoimmune disorders). The combination of these symptoms makes hypothyroidism a strong candidate for the single most likely diagnosis.

Other Likely Diagnoses

• Systemic Lupus Erythematosus (SLE): SLE can present with a wide range of symptoms including polyarthralgias, rash (often a malar rash), hair loss, and fatigue. Weight gain can also occur due to increased appetite or as a side effect of corticosteroid treatment.
• Rheumatoid Arthritis (RA): While RA primarily causes joint symptoms like polyarthralgias, it can also be associated with fatigue, weight gain, and less commonly, hair loss and rash. The presence of a rash could suggest a related condition or an overlap syndrome.
• Psoriatic Arthritis: This condition combines the swollen, scaly skin of psoriasis with joint pain and arthritis. Patients may experience fatigue, weight gain, and hair loss, especially if they have a significant psoriatic rash.

Do Not Miss Diagnoses

• Addison's Disease: Although rare, Addison's disease (primary adrenal insufficiency) can present with fatigue, weight loss (but sometimes gain), and skin hyperpigmentation that might be mistaken for a rash. Hair loss can also occur. This diagnosis is critical to consider due to its potential for life-threatening adrenal crisis.
• Cancer (e.g., Lymphoma): Certain types of cancer, such as lymphoma, can cause a wide range of systemic symptoms including fatigue, weight gain or loss, hair loss, and rash. It's crucial to consider malignancy in the differential diagnosis to ensure timely and appropriate treatment.

Rare Diagnoses

• Sjögren's Syndrome: This autoimmune disorder primarily affects the glands that produce tears and saliva but can also cause fatigue, joint pain, rash, and hair loss. While less common, it should be considered in patients with a combination of these symptoms.
• Dermatomyositis: Characterized by skin rash and muscle weakness, dermatomyositis can also present with fatigue, weight gain, and hair loss. It's a rare condition but important to diagnose due to its association with underlying malignancy and the need for specific treatment.