What are the differential diagnoses for a patient with reddish-brown, telangiectatic (telangiectasia) macules and patches mainly on the right limb, associated with flushing, itching, and burning, with an initial consideration of telangiectatic macularis eruptiva perstans (TMEP)?

Differential Diagnoses for Reddish-Brown Telangiectatic Lesions with Flushing, Itching, and Burning

Your primary consideration of telangiectasia macularis eruptiva perstans (TMEP) is appropriate, but you must also consider urticaria pigmentosa, diffuse cutaneous mastocytosis, rosacea, and hereditary hemorrhagic telangiectasia in your differential diagnosis.

Primary Differential: Other Forms of Cutaneous Mastocytosis

Urticaria Pigmentosa (UP)

• UP is the most common form of cutaneous mastocytosis and presents with reddish-brown macules and patches on the trunk and extremities, similar to TMEP 1
• Key distinguishing feature: Darier's sign (urtication and flare upon rubbing lesions) is typically positive in UP, though not universally present 1
• UP lesions can coexist with TMEP, making differentiation challenging 1
• Flushing, pruritus, and burning are common mast cell mediator-related symptoms in UP, occurring in 20-65% of cases 1
• Histopathology shows increased mast cells in papillary dermis aggregating around blood vessels 1

Diffuse Cutaneous Mastocytosis (DCM)

• DCM is rare (1-3% of cutaneous mastocytosis cases) but presents with more extensive skin involvement 1
• Characterized by whole body flushing, severe pruritus, and potential systemic symptoms including hypotension and diarrhea 1
• The skin may appear leathery and thickened with prominent dermatographism 1
• This diagnosis becomes more likely if symptoms are severe or if there is extensive body surface area involvement 1

Secondary Differential: Rosacea

Cutaneous Rosacea

• Persistent centrofacial erythema with telangiectasia and periodic intensification by trigger factors is diagnostic of rosacea 2, 3
• Telangiectasia on cheeks, nose, and ears represents a major feature 2
• Associated with burning and stinging sensations, similar to your patient's symptoms 2, 3
• However, rosacea typically has centrofacial distribution, not unilateral limb involvement, making this less likely in your case 2, 3
• Flushing is triggered by exercise, outdoor exposure, and other environmental factors 2, 3

Ocular Rosacea Consideration

• If facial involvement is present, evaluate for ocular symptoms including burning, stinging, dryness, or recurrent styes 1, 2
• Ocular rosacea can lead to sight-threatening complications if untreated 1, 2

Tertiary Differential: Hereditary Hemorrhagic Telangiectasia (HHT)

• Multiple telangiectasias at characteristic sites (lips, oral cavity, fingers, nose) constitute diagnostic criteria for HHT 4
• Epistaxis typically begins around age 11 years in HHT type 1 4
• The unilateral limb distribution in your patient makes HHT less likely, as HHT typically presents with multiple characteristic site involvement 4

Critical Distinguishing Features to Assess

Clinical Examination

• Test for Darier's sign by firmly stroking a lesion—positive urtication suggests mastocytosis (UP or TMEP) 1
• Assess distribution pattern: TMEP typically involves trunk and extremities symmetrically 5, 6, 7
• Your patient's unilateral right limb predominance is atypical for classic TMEP, which usually presents symmetrically 6
• Examine for facial involvement to evaluate for rosacea 2, 3
• Look for mucosal telangiectasias (lips, oral cavity) to assess for HHT 4

Symptom Characterization

• Document flushing episodes: frequency, duration, triggers, and associated symptoms 1, 5
• Assess for gastrointestinal symptoms (abdominal pain, diarrhea) suggesting systemic mastocytosis 1, 5
• Inquire about syncope, palpitations, or hypotensive episodes indicating systemic involvement 5

Diagnostic Workup

• Skin biopsy with mast cell staining (tryptase and chymase) is essential to confirm mastocytosis and differentiate TMEP from UP 1
• Serum tryptase level to assess for systemic mastocytosis 5
• If systemic symptoms are present, consider bone marrow biopsy and evaluation for visceral involvement 1, 5

Common Pitfalls to Avoid

• Do not dismiss the diagnosis of mastocytosis based on absence of Darier's sign alone—it is not present in all patients 1
• Do not overlook systemic symptoms; TMEP can be associated with systemic mastocytosis requiring medical management 5, 7
• Unilateral or asymmetric presentation does not exclude mastocytosis—variants exist 7
• In darker skin tones, telangiectasia and erythema may be difficult to visualize, requiring greater emphasis on symptoms and hyperpigmentation 1, 3