Multiple myeloma (MM) is a cancer of plasma cells, a type of white blood cell, that primarily develops in the bone marrow. While its main effects are seen in the bones, blood, and kidneys, MM can also manifest on the skin, though this occurs in a minority of patients. These skin changes, often described as a rash or lesions, can be a direct result of the cancerous cells or a secondary complication of the abnormal proteins they produce. Recognizing these skin symptoms is important for identifying potential disease progression or complications.
The Appearance of Direct Multiple Myeloma Skin Lesions
The most direct form of skin involvement occurs when malignant plasma cells spread from the bone marrow and infiltrate the skin, a condition known as cutaneous plasmacytoma. These lesions are rare but highly specific, often indicating an aggressive or advanced stage of the disease. They present as distinct, localized growths rather than a widespread rash.
These growths usually appear as nodules or firm plaques that are rubbery to the touch. They are frequently reddish-brown, violaceous, or purplish, but can sometimes be skin-colored. They commonly range from one to five centimeters in diameter and may be solitary or multiple.
Common sites include the trunk, abdomen, head, scalp, face, and limbs. Because they represent an accumulation of tumor cells, they may be tender or painful to the touch. The presence of these specific lesions warrants immediate medical investigation as they are a definitive sign of the underlying plasma cell malignancy.
Indirect Skin Conditions Linked to Multiple Myeloma
Skin problems are more commonly caused by complications arising from the abnormal proteins, called paraproteins or M-proteins, produced by the myeloma cells. These secondary conditions often manifest as a rash or unusual skin discoloration. The deposition of these proteins in tissue or their effect on blood vessel function leads to distinct appearances.
Amyloidosis
One such condition is amyloidosis, where light-chain paraproteins deposit as an insoluble, waxy substance in the skin and blood vessel walls. This deposition results in a distinctive appearance of waxy, translucent papules or plaques, often found around the eyes or in skin folds.
A classic sign is periorbital purpura, or “raccoon eyes,” which presents as bruising and bleeding around the eyes. This bruising is frequently triggered by minor actions like rubbing or straining.
Another complication is cryoglobulinemia, which occurs when certain paraproteins clump together in cooler temperatures, causing inflammation of small blood vessels (vasculitis). This results in a rash of palpable purpura—raised, non-blanching red or purple spots—most often seen on the lower extremities. Reduced blood flow can also lead to livedo reticularis, a mottled, net-like pattern of blue or purple discoloration. In severe cases, painful necrotic ulcers may develop.
In cases of hyperviscosity syndrome, excessive M-proteins significantly thicken the blood, slowing circulation. While this primarily causes neurological and visual symptoms, the skin can be affected by easy bruising and purpura due to fragile blood vessel walls. This excessive bleeding or bruising, particularly from mucosal surfaces, can be an initial indicator of the thick, sluggish blood flow.
Why Multiple Myeloma Causes Skin Problems
The three main pathways for skin manifestations trace directly back to the nature of the plasma cell cancer. The rarest cause is the direct infiltration of the skin by the malignant plasma cells, forming cutaneous plasmacytomas. These cancerous cells migrate from the bone marrow to soft tissue, creating tumor masses visible on the skin.
The more common secondary skin issues stem from the overproduction of paraproteins, the abnormal antibodies produced by the myeloma cells. In amyloidosis, these light chain proteins misfold and build up in the dermis and surrounding blood vessels, creating the waxy papules and causing vessels to become fragile and prone to rupture. In cryoglobulinemia, the paraproteins congeal at lower temperatures, clogging small vessels and triggering an inflammatory response.
A third factor is the immune dysregulation caused by the disease itself and its treatments. Multiple myeloma suppresses the body’s normal immune response, leaving patients highly susceptible to infections that manifest as rashes. A common example is the reactivation of the varicella-zoster virus, which presents as herpes zoster (shingles). Shingles is characterized by a painful, blistering rash in a localized band. The underlying malignancy and many anti-myeloma therapies contribute to this state of immune vulnerability.
Seeking Diagnosis and Treatment for Skin Symptoms
Any new or worsening rash or unusual skin growth in a person with multiple myeloma should be brought to the attention of an oncologist or dermatologist immediately. The appearance of a skin lesion can signal a serious complication or progression of the underlying cancer. Prompt consultation is necessary to determine the specific cause and guide appropriate management.
The diagnostic process often involves a skin biopsy, where a small sample of the affected tissue is removed and examined under a microscope. This is done to confirm the presence of either malignant plasma cells in the case of a plasmacytoma, or amyloid deposits using specialized stains. Blood tests are also performed to measure the concentration of M-proteins and to detect the presence of cryoglobulins.
Treating the underlying multiple myeloma is the ultimate approach to resolving the associated skin symptoms. Successful treatment of the cancer with chemotherapy or other anti-myeloma therapies usually leads to a decrease in the abnormal protein load or a reduction in the tumor burden, subsequently clearing the skin manifestations. However, secondary conditions like cryoglobulinemia or infections may also require specific, targeted treatment, such as plasma exchange or antiviral medication.