Differential Diagnosis

The patient presents with a complex set of symptoms that include initial severe pain in the back, hips, and ankles, which improved rapidly but unevenly, leaving residual pain in one toe and an ankle. Additionally, the patient experiences gum irritation to the point of limited mouth opening. The connection between these symptoms, their likelihood of being related or separate, and potential diagnoses are explored below.

1. Likelihood of Connection

The symptoms could be connected, especially considering the rapid onset and improvement of the joint pain, followed by gum irritation. This sequence suggests a systemic or autoimmune process.

2. Likelihood of Separate Conditions

It's also plausible that the joint pain and gum irritation are separate conditions, given their distinct nature and the uneven healing of the joint pain.

3. Most Likely Explanation if Related

If the symptoms are related, the most likely explanation could involve an autoimmune or inflammatory condition that affects both joints and mucous membranes.

4. Most Likely Explanation if Separate

If separate, the joint pain could be attributed to a condition like rheumatoid arthritis or a viral arthropathy, while the gum irritation might be due to a dental issue or a condition like temporomandibular joint (TMJ) disorder.

Differential Diagnoses

Single Most Likely Diagnosis

• Reactive Arthritis: This condition can follow a gastrointestinal or genitourinary infection, leading to asymmetric arthritis, and can also involve mucous membranes, potentially explaining both the joint pain and gum irritation.

Other Likely Diagnoses

• Rheumatoid Arthritis (RA): Although RA typically presents with symmetric joint involvement, it can start asymmetrically and involves mucous membranes, which could explain the gum irritation.
• Viral Arthropathy: Certain viral infections can cause arthralgias and myalgias that improve rapidly but can leave residual pain in some joints.
• Temporomandibular Joint (TMJ) Disorder: Could explain the gum irritation and limited mouth opening but doesn't directly account for the initial widespread joint pain.

Do Not Miss

• Lyme Disease: Can cause arthritis and, in rare cases, involvement of mucous membranes. It's crucial to consider due to its potential for serious complications if untreated.
• Gonococcal Arthritis: A bacterial infection that can cause septic arthritis and also involves mucous membranes, making it a critical diagnosis not to miss.

Rare Diagnoses

• Relapsing Polychondritis: A rare autoimmune disorder that can affect cartilage and connective tissue, potentially explaining both joint and mucous membrane symptoms.
• Sjögren's Syndrome: An autoimmune disorder that primarily affects the glands that produce tears and saliva but can also cause arthritis and mucous membrane irritation.

Each of these diagnoses is considered based on the patient's presentation, with an emphasis on those conditions that could plausibly explain both the joint pain and the gum irritation, as well as those that are critical not to miss due to their potential for serious complications.