Differential Diagnosis

The patient presents with a combination of symptoms including red and purple discoloration of the feet, pain, dark vision spots, cough, and a history of Rheumatoid Arthritis (RA). Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Vasculitis associated with Rheumatoid Arthritis: Given the patient's history of RA, the presence of red and purple discoloration (which could indicate vasculitic rashes or purpura), pain, and other systemic symptoms like cough, suggests a vasculitic process related to RA. Vasculitis can affect various sizes of blood vessels and can present with a wide range of symptoms depending on the organs involved.

• Other Likely Diagnoses

  • Interstitial Lung Disease (ILD) with associated pulmonary hypertension: This condition can cause cough and, if severe, might lead to hypoxia, which could potentially cause dark vision spots. ILD is a known complication of RA.
  • Methotrexate-induced lung disease: If the patient is on methotrexate for RA, this could be a cause of cough and potentially other symptoms, given methotrexate's known pulmonary side effects.
  • Sjögren's syndrome: Sometimes associated with RA, Sjögren's can cause a variety of systemic symptoms including dry eyes (which might lead to vision disturbances) and potentially skin manifestations.

• Do Not Miss Diagnoses

  • Giant Cell Arteritis (GCA): Although less likely given the specific symptoms, GCA is a condition that can cause vision disturbances (including dark spots) and is associated with polymyalgia rheumatica and sometimes RA. Missing GCA could lead to irreversible vision loss.
  • Antiphospholipid Syndrome (APS): This condition can cause a wide range of symptoms including thrombocytopenia (leading to purpura), vision disturbances due to retinal vascular occlusions, and could be associated with RA. APS can be life-threatening if not recognized and treated.
  • Sepsis or Infection: Any patient with a chronic condition like RA, especially if on immunosuppressive therapy, is at increased risk of infections. Sepsis can present with a wide range of non-specific symptoms including pain, cough, and vision changes due to hypoperfusion.

• Rare Diagnoses

  • Cryoglobulinemia: A condition characterized by the presence of cryoglobulins (proteins that precipitate from blood at cold temperatures) that can cause vasculitis, skin lesions, and potentially other systemic symptoms.
  • Churg-Strauss Syndrome (Eosinophilic Granulomatosis with Polyangiitis, EGPA): A form of vasculitis that can present with asthma, eosinophilia, and various systemic symptoms including skin and pulmonary manifestations. It's less common but could be considered in a patient with RA and these symptoms.