A woman has isolated hyperpigmentation of the distal fingertips and early‑morning stiffness of that hand; what is the most likely diagnosis and recommended work‑up?

Systemic Sclerosis (Scleroderma) with Digital Hyperpigmentation and Morning Stiffness

The most likely diagnosis is systemic sclerosis (scleroderma), specifically limited cutaneous systemic sclerosis, and the patient requires urgent rheumatology referral within 6 weeks along with immediate screening for internal organ involvement including pulmonary function testing, Doppler echocardiography, and high-resolution chest CT. 1, 2

Key Diagnostic Features Present

Distal fingertip hyperpigmentation ("darkening") in scleroderma represents skin thickening and fibrosis that characteristically begins at the fingers and progresses proximally. 3, 2

• Limited cutaneous systemic sclerosis presents with skin thickening confined to the hands and distal extremities, which matches this patient's isolated hand involvement 1, 3
• The hyperpigmentation reflects the fibrotic changes and microvascular damage that are hallmarks of scleroderma 2
• Morning stiffness lasting sufficient duration to be notable indicates inflammatory arthritis component, which occurs commonly in early systemic sclerosis with constitutional symptoms, arthritis, and marked hand swelling 3

Critical Distinguishing Features from Other Inflammatory Arthritides

This presentation differs fundamentally from rheumatoid arthritis or psoriatic arthritis because the primary complaint is skin darkening/thickening rather than joint swelling, and the distribution is limited to fingertips. 4, 5

• Rheumatoid arthritis characteristically targets metacarpophalangeal and proximal interphalangeal joints with visible synovitis in a symmetric pattern, not isolated fingertip skin changes 5, 6
• Morning stiffness ≥60 minutes with visible joint swelling would indicate inflammatory arthritis requiring different workup, but this patient's primary manifestation is cutaneous 4, 5
• The absence of Raynaud's phenomenon, capillaroscopic abnormalities, or scleroderma-specific autoantibodies would argue against scleroderma, but these should be actively sought 7

Immediate Diagnostic Workup Required

Order scleroderma-specific autoantibodies immediately, including anticentromere antibodies (associated with limited cutaneous disease) and anti-Scl-70 antibodies. 1, 2

• Anticentromere antibodies are characteristic of limited cutaneous systemic sclerosis and help predict disease course 1, 3
• Anti-RNA polymerase III antibodies indicate higher risk for scleroderma renal crisis and require blood pressure monitoring 1
• Inflammatory markers (ESR and CRP) should be obtained but may be normal in scleroderma unlike typical inflammatory arthritis 2

Perform nailfold capillaroscopy to detect the microvascular changes pathognomonic for systemic sclerosis. 7, 2

• Capillaroscopic abnormalities are diagnostic clues that differentiate scleroderma from scleroderma mimics 7
• The presence of dilated capillary loops and capillary dropout supports systemic sclerosis diagnosis 2

Mandatory Organ-Specific Screening

All patients with suspected systemic sclerosis require immediate screening for life-threatening internal organ involvement, even when presenting with seemingly isolated hand symptoms. 1, 2

• Pulmonary function testing with DLCO measurement is mandatory because interstitial lung disease occurs in 40-75% of patients and is progressive in 15-18% 1
• Doppler echocardiography must be performed to screen for pulmonary arterial hypertension, which is a life-threatening complication particularly in limited cutaneous disease 1, 3
• High-resolution chest CT should be obtained when pulmonary function tests are abnormal or clinical suspicion is high 1, 2
• Blood pressure monitoring is essential, especially if anti-RNA polymerase III antibodies are positive, to detect scleroderma renal crisis early 1

Assessment for Raynaud Phenomenon

Specifically question the patient about cold-induced color changes in the fingers (white, blue, then red), as Raynaud phenomenon occurs in nearly all systemic sclerosis patients and often precedes other symptoms by years in limited cutaneous disease. 1, 3, 2

• Limited cutaneous scleroderma patients typically have a long history of Raynaud phenomenon before other symptoms develop 3
• Raynaud phenomenon in systemic sclerosis should be treated with calcium channel blockers as first-line therapy, then phosphodiesterase-5 inhibitors or intravenous iloprost 1
• Digital ulcers occur in half of systemic sclerosis patients and require aggressive management to prevent complications 1, 8

Rheumatology Referral Urgency

Refer to rheumatology within 6 weeks regardless of whether morning stiffness meets the ≥60-minute threshold for inflammatory arthritis, because the skin changes themselves indicate systemic disease requiring specialist evaluation. 1, 4

• Early intervention can change the natural history of organ-based complications in systemic sclerosis 1
• The rheumatologist will coordinate multidisciplinary screening and determine whether disease-modifying therapy is indicated 1, 2
• For early diffuse cutaneous systemic sclerosis with high-risk features, autologous hematopoietic stem cell transplantation can improve survival 1

Common Pitfalls to Avoid

Do not dismiss isolated hand symptoms as benign or delay workup waiting for more obvious systemic manifestations, because internal organ involvement may already be present and progressive. 1, 2

• Limited cutaneous systemic sclerosis can have life-threatening complications from pulmonary hypertension and small intestine hypomotility despite appearing milder than diffuse disease 3
• Patients with scleroderma have poorly vascularized tissue and deficient soft tissue envelope, making any future surgical intervention particularly challenging 8, 9
• Do not confuse this presentation with vitiligo (depigmentation rather than hyperpigmentation with skin thickening) or other sclerodermoid disorders that lack Raynaud phenomenon and scleroderma-specific autoantibodies 1, 7

Initial Symptomatic Management While Awaiting Rheumatology

Initiate calcium channel blocker therapy (e.g., nifedipine extended-release 30-60 mg daily) if Raynaud phenomenon is present, as this is first-line treatment and can reduce digital ulcer development. 1

• Lifestyle modifications including avoiding cold exposure and smoking cessation are essential 2
• Proton pump inhibitor therapy should be started if any symptoms of gastroesophageal reflux are present, as esophageal dysmotility occurs in nearly 90% of systemic sclerosis patients 1, 3
• Avoid high-dose corticosteroids as they increase risk of scleroderma renal crisis 2