What is the diagnosis of lesions on the palms and soles of a patient with a history of psoriasis on the knees?

Diagnosis: Secondary Syphilis Until Proven Otherwise

The red and brown macules on the palms and soles developing over several weeks in this patient most likely represent secondary syphilis, not palmoplantar psoriasis, and require immediate serologic testing (RPR/VDRL and treponemal-specific tests) before assuming these lesions are psoriatic. 1

Critical Diagnostic Reasoning

Why This is Likely Secondary Syphilis

• The acute onset over "several weeks" is fundamentally inconsistent with psoriasis, which follows a chronic, stable course or gradual progression over months to years 1

• The American Academy of Dermatology specifically recommends serologic testing for syphilis in patients presenting with symmetric palmoplantar involvement with red-brown macules, due to the high likelihood of secondary syphilis 1

• The CDC guidelines emphasize that the temporal pattern—acute onset over weeks—strongly suggests secondary syphilis rather than a chronic inflammatory dermatosis like psoriasis 1

The Psoriasis History is a Red Herring

• While this patient has documented psoriasis on the knees, the presence of psoriasis elsewhere does not mean all new skin lesions are psoriatic 1

• Palmoplantar psoriasis typically presents with erythematous, scaly, hyperkeratotic plaques with fissuring—not red-brown macules 2

• Patients with chronic inflammatory conditions like psoriasis can still acquire sexually transmitted infections, and the CDC recommends HIV screening alongside syphilis testing as these infections frequently coexist 1

Immediate Diagnostic Workup Required

Essential Testing

• RPR or VDRL (nontreponemal test) plus treponemal-specific testing (FTA-ABS or TP-PA) to confirm active syphilis 1

• HIV screening, as syphilis and HIV frequently coexist and HIV status affects treatment decisions 1

• Consider skin biopsy only if serologic testing is negative and the diagnosis remains unclear 3

If Syphilis is Confirmed

• Benzathine penicillin G 2.4 million units IM as a single dose is the standard treatment for secondary syphilis 1

• Partner notification and treatment of sexual contacts is mandatory 1

• Follow-up serology at 3,6, and 12 months to confirm treatment response (expect 4-fold decline in RPR/VDRL titers) 1

If Serologic Testing is Negative: Consider Palmoplantar Psoriasis

Diagnostic Features of True Palmoplantar Psoriasis

• Erythematous, scaly, hyperkeratotic plaques with fissuring—not smooth red-brown macules 2

• Chronic, stable course over months to years 1

• Often recalcitrant to standard psoriasis treatments 4

Treatment Approach for Confirmed Palmoplantar Psoriasis

First-line therapy:

• High-potency topical corticosteroids under occlusion combined with calcipotriene ointment 1, 5

Second-line therapy if topicals fail:

• Oral acitretin 25 mg daily, with substantial improvement expected within 2 months 1, 5
• Soak PUVA therapy (topical psoralen followed by UVA exposure) 2-3 times weekly 1, 5

Third-line therapy for refractory cases:

• Biologic agents (adalimumab, infliximab, ustekinumab, or anti-IL-17/IL-23 agents) 1, 5

Critical Pitfalls to Avoid

• Never assume new palmoplantar lesions are psoriatic simply because the patient has psoriasis elsewhere—the clinical presentation and time course must match 1

• Avoid systemic corticosteroids as monotherapy in any form of psoriasis, as they can trigger severe flares including potentially life-threatening generalized pustular psoriasis 1

• Be aware that TNF-alpha antagonists can paradoxically induce pustular psoriasis of palms and soles, even in patients without prior pustular disease 1

• Do not confuse palmoplantar plaque psoriasis with palmoplantar pustulosis (PPP)—these are distinct entities with different treatment considerations 6, 7