What causes blue toenails?

Causes of Blue Toenails

Blue toenails result from three primary mechanisms: decreased arterial flow (most commonly from atheroembolic disease or thrombotic occlusion), impaired venous outflow, or abnormal circulating blood, with the critical distinction being whether the discoloration is blanching or non-blanching to guide diagnosis and prevent life- or limb-threatening complications. 1

Primary Diagnostic Categories

Decreased Arterial Flow (Most Common)

• Atheroembolic disease represents the most frequent cause of blue toe syndrome, where cholesterol emboli from proximal atherosclerotic plaques occlude digital arteries 1, 2
• Thrombotic occlusions can occur in polycythemia vera with thrombocythemia, causing arteriographically documented digital artery occlusions even without preexisting atherosclerotic disease 3
• Systemic sclerosis can present as blue toe syndrome as the primary manifestation, mediated by small vessel disease and vasospasm 2
• Peripheral vascular disease with reduced circulation increases susceptibility to ischemic changes 4

Impaired Venous Outflow

• Venous obstruction or insufficiency can cause blue-purple discoloration due to blood pooling 1
• This mechanism typically produces more diffuse, persistent discoloration 1

Abnormal Circulating Blood

• Polycythemia vera with thrombocythemia causes microvascular thrombotic lesions leading to red, purple, blue, or black toes through platelet-mediated occlusion 3
• Increased hematocrit contributes to progression from microvascular symptoms to major occlusive ischemic events 3

Secondary Causes to Consider

Medication-Induced Discoloration

• Minocycline, zidovudine, and hydroxyurea are frequently associated with polydactylic (multiple nail) blue discoloration 5
• These typically affect multiple nails bilaterally 5

Toxic and Exogenous Exposures

• Silver exposure can cause blue-gray nail discoloration affecting multiple nails 5
• Occupational exposures may contribute to underlying vascular disease 2

Systemic Diseases

• HIV/AIDS and systemic lupus erythematosus are associated with polydactylic blue nail discoloration 5
• These conditions often present with other systemic manifestations 5

Structural Lesions (Single Nail Involvement)

• Glomus tumors are the most common cause of monodactylic blue discoloration 5
• Blue nevi and melanomas must be ruled out when single nail involvement occurs 5
• Subungual hematoma from trauma causes blue-black discoloration that grows out with the nail 1

Critical Diagnostic Approach

History and Physical Examination Priorities

• Determine if discoloration is blanching or non-blanching by applying pressure—blanching suggests arterial insufficiency, while non-blanching indicates hemorrhage or pigment deposition 1
• Assess for pain—painful blue toes suggest acute ischemia requiring urgent evaluation 1, 3
• Count affected digits—single nail involvement suggests local pathology (tumor, trauma), while multiple nails suggest systemic cause (medication, systemic disease) 5
• Evaluate peripheral pulses and capillary refill to assess arterial perfusion 1
• Check for accompanying symptoms including fever, cold sensitivity, or other skin manifestations 2

Essential Laboratory and Imaging Studies

• Complete blood count to evaluate for polycythemia vera or thrombocythemia 3
• Autoimmune serologies including anticentromere antibodies if systemic sclerosis suspected 2
• Vascular imaging (arteriography or duplex ultrasound) when arterial occlusion suspected 1, 3
• Dermoscopy or biopsy for single nail involvement to rule out malignancy 5

Common Pitfalls to Avoid

• Do not dismiss blue toes as benign without thorough evaluation—many causes are life- or limb-threatening including atheroembolic disease, malignancy, and systemic vasculitis 1, 5
• Do not confuse with fungal infection—onychomycosis causes thickening, yellowing, and friable texture, not blue discoloration 4, 6
• Do not overlook medication history—polydactylic blue discoloration often has iatrogenic causes that are reversible 5
• Do not delay vascular evaluation in painful blue toes—acute arterial occlusion requires urgent intervention to prevent tissue loss 1, 3
• In polycythemia vera patients, recognize that standard anticoagulation and phlebotomy alone are insufficient—aspirin is essential for platelet-mediated microvascular symptoms 3