Side Effects And Risks Of Photodynamic Therapy

Photodynamic therapy is considered to be a safe and effective treatment for skin conditions and certain types of cancer. Like any medical procedure, photodynamic therapy carries the risk of side effects, although there are no known long-term side effects when administered properly. Read on to understand more about photodynamic therapy – what it is, what is involved, what the potential side effects are, and what the risks are.

Introduction

Photodynamic therapy (PDT) is a type of light therapy where a light source and a light-sensitive medication are used to kill abnormal cells.¹ The light-sensitive medication, called a photosensitiser, is activated in the presence of a specific type of light, most commonly from a laser or the sun. The photosensitiser is harmless on its own before activation and is taken up by cells.

When the photosensitiser is activated by a specific wavelength of light, it produces a harmful form of oxygen, called reactive oxygen species, that kills abnormal cells.² Photodynamic therapy is used in the treatment of skin conditions (acne, psoriasis), eye conditions (age-related macular degeneration) and several types of cancer.^3,4

Indications for photodynamic therapy 

Photodynamic therapy can be used to treat parts of the body where light can reach. These areas include the skin, mouth, eyes, lungs and oesophagus (food pipe). The following conditions are treated with photodynamic therapy.

Photodynamic therapy for skin conditions

• Psoriasis – an autoimmune skin disorder in which your skin is covered with dry, scaly patches³ 
• Actinic keratosis – a precancerous skin condition caused by years of exposure to sunlight that manifests as a rough or scaly patch of skin
• Acne – a common skin condition where pores become clogged causing the formation of whiteheads, blackheads, and other pimples. Photodynamic therapy is only used to treat acne if other conventional treatments have not been effective³
• Vitiligo – a skin disorder where parts of the skin lose their pigment resulting in white or light patches³
• Bowen’s disease – a very early, slow-growing form of skin cancer that is characterised by red, scaly skin patches

Photodynamic therapy for cancer

Photodynamic therapy is a minimally invasive treatment for several types of cancer. Photosensitiser drugs are selective and can be targeted to only kill cancer cells whilst preserving healthy tissue, which is highly beneficial in the case of cancer treatment. The following types of cancer can be treated with photodynamic therapy.⁴

• Skin cancer
• Esophageal cancer
• Lung cancer
• Bile duct cancer
• Bladder cancer
• Brain cancer
• Head and neck cancer
• Pancreatic cancer

What happens during photodynamic therapy?

There are two types of photodynamic therapy—conventional PDT and daylight PDT— depending upon the light source that is used. Conventional PDT uses a laser or lamp and is performed as an outpatient procedure. Daylight PDT uses natural daylight and can be carried out at home.⁵ 

During the first stage of therapy, your healthcare provider will administer the photosensitising drug. Depending on the condition being treated, the light-sensitive medicine may be given either in the form of a pill, through your vein (intravenously) or applied onto your skin as a cream or gel. The photosensitiser becomes concentrated in abnormal cells and makes them more sensitive to light.⁵

After the photosensitiser has been administered, your healthcare provider will use a specific light source to irradiate the area being treated. The light source differs depending on the treatment area and it may be natural daylight, blue light, or a low-power red laser light. Your healthcare provider will use an endoscope to shed light on the cells located inside of your body if the treatment areas include your lungs, airway or throat. In the presence of light, the photosensitiser will react with oxygen and cause a chemical reaction that destroys abnormal cells.² 

Side effects of photodynamic therapy

Photodynamic therapy has some side effects that vary depending on the area treated.⁶ Although the main target of photodynamic therapy is abnormal cells, the photosensitiser can also affect the healthy cells and therefore make you more sensitive to light even after the completion of the treatment. The side effects of photodynamic therapy are described in the following section.

Pain or discomfort

Pain at the treatment site is the most common side effect of PDT, reported by almost 60% of patients. Many patients experience a painful burning sensation during the light exposure which starts immediately, peaks after a few minutes, and subsides towards the end of the treatment.⁶ Pain during the procedure may be managed with cold air analgesia (a cooling spray), a fan to cool the skin, and local or topical anaesthetics applied prior to or following treatment. Daylight PDT is significantly less painful than conventional PDT.⁵ 

Inflammation

Post-treatment, the skin may become red, itchy, and swollen. Inflammation (red and puffy skin) is a normal reaction to photodynamic therapy and should improve by itself within a few days. It is recommended to avoid anti-inflammatory pain relief medication like ibuprofen which can suppress the body’s natural inflammatory response that also acts to kill abnormal cells.⁷

Skin effect

For skin treatments, it is common for the treated area to develop blisters, scales or discolouration. The skin may become covered with scales and blisters, weep, or become discoloured (slightly darker or lighter). The crusting of your skin heals after about 4 weeks. The stinging or burning sensation usually goes away immediately after PDT (or within 1 to 2 days). Hyperpigmentation is rare and generally resolves itself within a few months. Hypopigmentation can also occur in some cases but is less well understood. In extremely rare cases, PDT can cause permanent scarring.^5,6

Photosensitivity

Your skin and eyes may continue to be sensitive to light for up to six weeks after photodynamic therapy, especially if the photosensitiser is administered as an injection or oral liquid. During this time, it is important to avoid direct sunlight or bright indoor lights and apply sunscreen regularly.¹

Lung and oesophagus photodynamic therapy

Internal photodynamic therapy for lungs or oesophagus treatments may result in chest pain, sore throat, slightly bloody phlegm, difficulty swallowing (dysphagia) and nausea and vomiting. In most cases, these side effects are temporary. However, seek medical help if you cough up blood or are experiencing difficulty breathing.² 

How to limit the side effects of photodynamic therapy

To limit the side effects of photodynamic therapy, you should consider the following after consulting with your healthcare provider. 

• Avoid direct sunlight, indirect sunlight (through curtains or windows) and bright indoor lights for the first few days after treatment. Light from television and computer screens is fine, however⁷
• Take pain relief medication like paracetamol or co-codamol if you experience pain after your treatment
• Keep the dressing clean and dry and change it as recommended by your healthcare provider
• Make sure to apply sunscreen before going out in the sun, taking care to re-apply it to the treated area every 2 to 3 hours⁵

Risks associated with photodynamic therapy

Photodynamic therapy is a very safe and effective treatment for certain types of cancer and other skin conditions. The side effects associated with PDT usually improve in the days, weeks and months after treatment with few long-term negative effects.⁶ It is possible to have an allergic reaction to the photosensitiser in very rare cases.

The treatment site may get infected after photodynamic therapy so it is important to keep the area clean and dry and follow all aftercare instructions. PDT is not recommended if you are pregnant or have a diagnosis of porphyria or lupus.^5,6

FAQs

What is photodynamic therapy and how does it work?

Photodynamic therapy is a type of light therapy, that involves the use of a photosensitive drug (light-sensitive medicine) and a light source producing light of a specific wavelength. Your healthcare provider will administer the photosensitiser (either through your vein, applied onto your skin, or orally depending on the area being treated). Then your healthcare provider will shine the light over the treatment site to activate the photosensitive drug, causing the destruction of abnormal cells.

What are the common side effects of photodynamic therapy?

Common side effects of photodynamic therapy include redness, swelling, and pain or discomfort at the treatment site. These side effects are temporary and will improve within 1–2 weeks.

Are there any risks associated with photodynamic therapy?

Photodynamic therapy is generally a safe procedure but like any other medical procedure, it also carries certain risks. Risks of photodynamic therapy include an allergy to photosensitiser (light-sensitive drug), prolonged sensitivity to light, scarring, and potential damage to surrounding healthy tissues.

How long do the side effects of photodynamic therapy last?

Although the recovery period varies and depends on the disease being treated as well as your response, most side effects are temporary and resolve within the first few weeks or months after photodynamic therapy. 

How should I care for the treated area?

For skin treatments, the treated area should be covered by a dressing immediately after the procedure. Keep the area clean and dry and change the dressing as directed by your healthcare provider. Refrain from scratching the treated site to avoid dislodging the scab during healing. Always apply sunscreen before going outside as your skin may be more sensitive to sunlight for several weeks after the procedure. 

Summary

Photodynamic therapy (PDT) is a type of light therapy that involves the use of a light-sensitive drug (photosensitiser) and a light source to kill abnormal cells. producing light of a specific wavelength. The photosensitiser is inactive and non-toxic. When the body is irradiated by light of a specific wavelength, the photosensitiser is activated and it produces reactive oxygen species which kill abnormal cells.

Photodynamic therapy is a non-invasive outpatient procedure that is used in the treatment of several skin conditions and types of cancer. As with any medical procedure, photodynamic therapy is accompanied by various side effects which are related to the area being treated. The onset and duration of side effects can vary from immediately following treatment, to within days, weeks, or months of treatment.

Skin side effects may include redness, swelling, burning, itching, blistering, scarring, discolouration, and scaling. The side effects of oesophageal or lung photodynamic therapy include a sore throat, chest pain, nausea, and bloody phlegm. After photodynamic therapy, the skin may become sensitive to bright lights and sunlight for some time and protecting the skin and eyes after the procedure is particularly important.