A 32-year-old woman presents the GP with six months of worsening pain and stiffness in her fingers bilaterally, particularly in the mornings. She works as a builder and is struggling to cope at work with the pain. She has become gradually more short of breath on exertion over recent months with a dry cough.

On examination there are fine bilateral inspiratory crackles in the chest, and bilateral swan neck deformity in the proximal interphalangeal and metacarpophalangeal joints.

Bloods are shown below

| Serum                                            | Result | Reference Range |
| ------------------------------------------------ | ------ | --------------- |
| Rheumatoid factor (RF)                           | 45     | <60 U/mL        |
| Anti-cyclic citrullinated peptide (CCP) antibody | 1      | <7 U/mL         |

Which of the following is the most likely diagnosis?

Options:
explanation: Limited cutaneous systemic sclerosis, previously named CREST syndrome, causes calcinosis, Raynaud's disease, oesophageal dysmotility, sclerodactyly, and telangiectasia. It may produce hard and thickened skin with non-pitting oedema of the fingers and toes (sclerodactyly). While it may result in joint pain and swelling with pulmonary fibrosis, the characteristic tenderness, inflammation, and swan neck deformity in the proximal interphalangeal and metacarpophalangeal joints is more typical of rheumatoid arthritis
name: Limited cutaneous systemic sclerosis
label: d
answer: no
explanation: The history and examination findings are most consistent with rheumatoid arthritis (chronic pain and stiffness in the morning) with extra-articular pulmonary fibrosis (exertional dyspnoea with end-inspiratory crackles on examination). Rheumatoid factor (RF) is positive in 60-70% of patients with rheumatoid arthritis. Anti-CCP antibody positive in 80% of patients with rheumatoid arthritis. There are a subgroup of patients with rheumatoid arthritis with negative RF and anti-CCP antibodies - known as seronegative rheumatoid arthritis. In these cases, diagnosis is made by x-ray findings with history and examination
name: Rheumatoid arthritis
label: a
answer: yes
explanation: Sarcoidosis presents with pyrexia, night sweats, malaise, and lethargy. The lungs are the most common organ to be affected with a restrictive pattern seen from diffuse parenchymal disease. It can affect virtually any organ, but in the joints, it often causes soft-tissue swelling, dactylitis, and tenosynovitis. It is less likely to present with swan neck deformity the proximal interphalangeal and metacarpophalangeal joints - this is more typical of rheumatoid arthritis
name: Sarcoidosis
label: b
answer: no
explanation: Systemic lupus erythematosus (SLE) is a multiorgan disease presenting with a wide range of signs and symptoms. The patients often have non-specific symptoms such as pyrexia, malaise, fatigue, lymphadenopathy, and arthralgia. Arthralgia can present as early morning stiffness in peripheral symmetrical joints along with SLE arthropathy with swan-neck deformity. It can less-commonly affect the lungs causing fibrosing alveolitis or obliterative bronchiolitis. While the patient is experiencing both of these issues, patients with SLE will usually display other constitutional symptoms. The characteristic tenderness, inflammation, and swan neck deformity in the proximal interphalangeal and metacarpophalangeal joints is more typical of rheumatoid arthritis
name: Systemic lupus erythematosus
label: c
answer: no
explanation: Reactive arthritis is an RF-seronegative, HLA-B27-linked inflammatory arthritis that develops in response to a recent infection. It usually develops following gastrointestinal infections such as _Salmonella_, _Shigella_, or _Campylobacter_ or genitourinary infections such as _Chlamydia trachomatis_. It is characterised by large joint asymmetric inflammatory oligoarthritis, conjunctivitis/uveitis, and urethritis/cervicitis (can't see, pee, or climb a tree). This patient does not complain of ocular symptoms, dysuria, or symptoms of urethritis and so reactive arthritis is less likely
name: Seronegative reactive arthritis
label: e
answer: no

Correct answer: a


Learning point: In patients with rheumatoid arthritis who test negative for rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies—referred to as seronegative rheumatoid arthritis—diagnosis is typically made based on clinical history, physical examination, and characteristic x-ray findings that show joint damage, erosions, and narrowing.