Differential Diagnosis

The patient's presentation is complex, involving multiple systems. Here's a breakdown of potential diagnoses categorized for clarity:

• Single Most Likely Diagnosis

  • Giant Cell Arteritis (GCA) with Polymyalgia Rheumatica (PMR) and Spinal Stenosis: This combination could explain the skin vasculitis, inflammation in the lower spine, chronic back pain, neurogenic claudication, and systemic symptoms like nausea, diarrhea, progressive weakness, lethargy, and confusion. GCA can lead to vasculitis, and PMR often presents with systemic inflammation and proximal muscle weakness. Spinal stenosis could account for the neurogenic claudication and back pain.

• Other Likely Diagnoses

  • Rheumatoid Arthritis (RA) with Secondary Sjögren's Syndrome: RA could explain the systemic inflammation, skin vasculitis, and joint symptoms. Secondary Sjögren's could contribute to gastrointestinal symptoms like nausea and diarrhea.
  • Systemic Lupus Erythematosus (SLE): SLE is known for its multi-system involvement, including skin vasculitis, arthritis, gastrointestinal symptoms, and neurological manifestations like confusion and weakness.
  • Multiple Myeloma with Amyloidosis: This could explain the progressive weakness, back pain (due to vertebral body fractures or infiltration), and systemic symptoms. Amyloidosis can cause gastrointestinal symptoms and neuropathy.

• Do Not Miss Diagnoses

  • Spinal Epidural Abscess: A medical emergency that could present with back pain, progressive weakness, and systemic symptoms like fever and confusion. Prompt diagnosis and treatment are crucial.
  • Cauda Equina Syndrome: Another neurological emergency that could explain the progressive lower extremity weakness, neurogenic claudication, and bowel/bladder dysfunction.
  • Vasculitis due to Infection (e.g., Endocarditis): Infectious causes of vasculitis, such as endocarditis, could present with systemic symptoms, skin findings, and multi-organ involvement.

• Rare Diagnoses

  • Ehlers-Danlos Syndrome with Vascular Complications: A genetic disorder that could lead to skin and vascular manifestations, although it's less likely to present acutely in this manner.
  • Sarcoidosis: While sarcoidosis can cause multi-system disease, the specific combination of symptoms and findings in this patient makes it less likely.
  • Primary Amyloidosis: Similar to the consideration in the "Other Likely Diagnoses" section but without a clear underlying plasma cell dyscrasia or other associated condition.