Differential Diagnosis

The patient's symptoms of recurring and fleeting pains in different large joints, IBS symptoms, occasional tendonitis, and generally bad mood, along with chronic feelings of not being well and negative repeated lab tests, suggest a complex clinical picture. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Fibromyalgia: This condition is characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues. The patient's symptoms of recurring pains in different joints, IBS symptoms, and bad mood, despite negative lab tests, align closely with fibromyalgia. The chronic use of ADHD meds sporadically might also contribute to or exacerbate symptoms.

• Other Likely Diagnoses

  • Rheumatoid Arthritis (RA): Although the patient has had negative lab tests, early or seronegative RA could still be a consideration, especially given the joint pains. However, the fleeting nature and involvement of different joints might be less typical.
  • Lupus: Systemic lupus erythematosus can present with joint pains, gastrointestinal symptoms, and mood changes. The lack of specific findings on lab tests does not rule out lupus, as it can be seronegative.
  • Hypermobility Syndrome: This condition involves joint hypermobility, which can lead to joint pains and possibly some of the other symptoms like tendonitis.

• Do Not Miss Diagnoses

  • Lyme Disease: Although less common, Lyme disease can cause joint pains, neurological symptoms, and mood changes. It's crucial to consider this, especially if the patient has been exposed to ticks.
  • Multiple Sclerosis (MS): MS can present with a wide range of symptoms, including pain, mood changes, and gastrointestinal issues. The diagnosis would require specific neurological findings and imaging.
  • Endocrine Disorders (e.g., Hypothyroidism): These can cause widespread symptoms including joint pains, mood changes, and gastrointestinal issues.

• Rare Diagnoses

  • Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. It could explain joint hypermobility and possibly some gastrointestinal symptoms.
  • Sjögren's Syndrome: An autoimmune disorder that can cause joint pain, gastrointestinal symptoms, and mood changes, though it's more commonly associated with dry eyes and mouth.
  • Sarcoidosis: A condition where inflammatory cells form lumps known as granulomas in various parts of the body, which can lead to a wide range of symptoms including joint pains and mood changes.

Treatment Approach

The treatment approach would depend on the confirmed diagnosis but may include:

• Fibromyalgia: Medications for pain and sleep, lifestyle changes, and possibly cognitive-behavioral therapy.
• Rheumatoid Arthritis or Lupus: Disease-modifying antirheumatic drugs (DMARDs), biologics, and lifestyle adjustments.
• Hypermobility Syndrome: Physical therapy, pain management, and lifestyle changes.
• Lyme Disease: Antibiotics.
• Multiple Sclerosis: Disease-modifying therapies.
• Endocrine Disorders: Hormone replacement therapy.
• Ehlers-Danlos Syndrome, Sjögren's Syndrome, Sarcoidosis: Treatment varies widely depending on the specific condition and symptoms but often involves managing symptoms and preventing complications.

Given the complexity and the need for a precise diagnosis to guide treatment, a comprehensive evaluation by a rheumatologist or a multidisciplinary team might be necessary.