MM is a cancer originating in the plasma cells of the bone marrow, a type of white blood cell responsible for producing antibodies. While the disease primarily affects the skeletal system and blood, it can manifest in the skin, often signaling systemic complications or advanced disease activity. These skin changes are diverse, ranging from minor bruising to painful lesions, and they arise from the disease process itself, its secondary effects, or the necessary treatments. Recognizing these dermatologic signs is important for both diagnosis and managing the overall health of a patient with MM.
Primary Skin Manifestations
The most common visible skin alterations are caused by bleeding beneath the surface, appearing as small, non-blanching spots called petechiae, or larger purple patches known as purpura. These lesions do not turn white when pressed, indicating the color is due to extravasated blood. This easy bruising often appears in areas of pressure or trauma, or in localized sites like the periorbital area, face, forearms, and hands.
Another distinct presentation is associated with Amyloid Light-chain (AL) amyloidosis, a complication where abnormal myeloma proteins deposit in the skin tissue. These deposits often look like smooth, slightly raised, waxy papules that can be flesh-colored or brownish. A characteristic location for these lesions is the periorbital region, sometimes causing a bruised appearance around the eyes known as “raccoon eyes.” They may also be found on the face and neck.
A more specific, though rare, manifestation is the cutaneous plasmacytoma, which is a direct infiltration of malignant plasma cells into the skin. These lesions are generally firm, reddish-brown nodules or tumors that may appear dome-shaped or as plaques. Plasmacytomas are considered the most specific skin sign of the underlying plasma cell disorder, though they are usually a late-stage finding.
Cryoglobulinemia, a condition linked to MM, can lead to painful, mottled, or ulcerated skin changes, primarily on the extremities. This condition involves abnormal proteins that clump together in cooler temperatures, restricting blood flow and causing small vessel inflammation called vasculitis. The resulting rash is often a palpable purpura—a raised, non-blanching purple rash—that can progress to painful, necrotic ulcers or even gangrene in severe cases.
Underlying Biological Mechanisms
Many visible skin symptoms are direct consequences of the abnormal processes driven by the cancerous plasma cells. The most straightforward mechanism involves thrombocytopenia, a reduced number of platelets necessary for clotting. When myeloma cells proliferate in the bone marrow, they can suppress the production of normal blood cells, including platelets. A low platelet count makes small vessels fragile, causing blood to leak into the skin easily, resulting in petechiae and purpura.
The abnormal proteins, known as M-proteins, produced by the myeloma cells are responsible for several systemic complications, including amyloidosis. These M-proteins (specifically the light-chain fragments) are misfolded and deposit as insoluble amyloid fibrils in various organs, including the dermis. This deposition causes the waxy, firm appearance and fragility of the skin associated with amyloidosis.
High concentrations of M-proteins can also increase the viscosity, or thickness, of the blood. This hyperviscosity slows blood flow, which can lead to poor circulation in the extremities and result in mottled skin or painful, blue-tinged discoloration. When these M-proteins are cryoglobulins—proteins that precipitate when exposed to cold—they trigger the vasculitis that causes the painful, deep purpura and potential tissue death seen in cryoglobulinemia.
Skin Changes Related to Treatment and Immunity
Beyond the direct effects of the cancer, many skin issues in MM arise from therapeutic interventions and the resulting weakened immune system. A common issue is the development of drug-induced rashes, which are reactions to chemotherapy and immunomodulatory agents. Medications like Bortezomib and Lenalidomide can cause generalized maculopapular rashes, consisting of flat, red areas (macules) and small, raised bumps (papules). These rashes can be intensely itchy and inflamed, usually appearing within the first few weeks of starting a new regimen.
The compromised immune status of patients with MM makes them highly susceptible to opportunistic infections, with viral reactivation being a frequent cause of skin eruptions. Herpes zoster, commonly known as shingles, is a particular concern, reactivating due to a weakened cell-mediated immune response. The shingles rash presents as painful clusters of vesicles (blisters) on a red base, strictly following the path of a single nerve (a dermatome), typically occurring on one side of the body.
Generalized itching, or pruritus, is another frequent complaint that may occur even without a visible rash. This symptom can be a side effect of certain treatments or a sign of underlying organ dysfunction. Kidney impairment, a common complication of MM, can cause a build-up of toxins that irritate nerve endings in the skin, leading to persistent and sometimes severe itching.
When to Seek Immediate Medical Attention
Any new or changing skin lesion in a patient with multiple myeloma warrants immediate discussion with the hematology or oncology team. Specific signs, however, indicate a situation requiring urgent medical consultation or an emergency room visit. These urgent signs include spreading redness, warmth, or increasing pain surrounding a rash or lesion, which can indicate a rapidly progressing bacterial infection.
The following signs require immediate attention:
- Sudden, widespread, and painful rash, especially if accompanied by a fever, chills, or blisters, which may signal a severe drug hypersensitivity reaction.
- Onset of large, rapidly expanding hematomas (bruises), or any bleeding from the nose or gums, suggesting a potentially dangerous drop in platelet counts.
- Necrotic ulcers, tissue death, or gangrene on the fingers, toes, or other extremities, particularly if associated with cold exposure, as these are symptoms of severe, life-threatening cryoglobulinemia.
- Any persistent or non-healing ulcer, or a skin lesion that quickly changes in size, color, or shape, should be brought to the attention of a doctor promptly.