Differential Diagnosis

The patient's presentation of mild osteopaenia, recent viral infection symptoms, and normal ultrasound findings for the shoulder and rotator cuff warrants a broad differential diagnosis. The following categories outline potential diagnoses:

• Single Most Likely Diagnosis

  • Post-viral fatigue syndrome or post-COVID-19 syndrome: Given the patient's recent history of viral infection symptoms consistent with COVID-19, such as mild fever, persistent headache, sore throat, and dry cough, and the timing of these symptoms, it is plausible that the patient is experiencing post-viral complications. These can include musculoskeletal pain, fatigue, and other systemic symptoms that do not necessarily correlate with specific findings on imaging or laboratory tests.

• Other Likely Diagnoses

  • Fibromyalgia: This condition is characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues. The patient's symptoms of persistent headache and sore throat, in addition to the musculoskeletal complaints, could align with fibromyalgia, especially if the post-viral syndrome is considered a trigger.
  • Osteomalacia: Although the DEXA scan showed mild osteopaenia, and the patient is on annual bisphosphonates, osteomalacia (softening of the bones due to defective bone mineralization) could be a consideration, especially if there are concerns about vitamin D deficiency or other metabolic bone diseases.

• Do Not Miss Diagnoses

  • Giant Cell Arteritis (GCA): Despite the ultrasound eliminating PMR (Polymyalgia Rheumatica) due to the lack of fluid in shoulders or hips, GCA, which often co-exists with PMR, is a critical diagnosis not to miss due to its potential for serious complications, including vision loss. The recent viral infection could potentially trigger an inflammatory response.
  • Multiple Myeloma: This is a type of blood cancer characterized by bone marrow proliferation of malignant plasma cells. It can cause bone pain, osteopaenia, or osteolytic lesions. Although less likely, given the mild osteopaenia and absence of other specific symptoms like anemia or renal failure, it is crucial not to miss this diagnosis due to its significant implications.

• Rare Diagnoses

  • Relapsing Polychondritis: A rare autoimmune disorder that can cause cartilage inflammation, leading to pain and other symptoms. It might be considered if the patient has additional symptoms like cartilaginous involvement or other autoimmune manifestations.
  • Sarcoidosis: A condition characterized by the growth of granulomas (inflammatory cells) in various parts of the body, which can lead to musculoskeletal symptoms among others. It is rare but could be a consideration if other systemic symptoms or findings suggestive of sarcoidosis are present.