SAPHO Syndrome - Causes, Clinical Features, Diagnosis, and Treatment

Introduction:

SAPHO is a chronic disorder that includes synovitis, acne, pustulosis, hyperostosis, and osteitis. It occurs in any age group but is more common among 30 and 50 years old. SAPHO syndrome was first investigated by a rheumatologist named Chamot in 1987.

What Is SAPHO Syndrome?

SAPHO syndrome includes:

1. Synovitis is characterized by pain, swelling, and stiffness of joints.

2. Acne occurs when dead skin cells are clogged within the hair follicles.

3. Pustulosis are large bubbles filled with pus, seen mainly on the palms and soles.

4. Osteitis is characterized by inflammation of bones along with tenderness and pain.

5. Hyperostosis is the excessive growth of bone.

What Causes SAPHO?

There are various factors that are involved in the SAPHO syndrome:

Environmental Components:

Several biopsies and bone culture studies show a strong connection between bacterial pathogens that cause skin and bone lesions of SAPHO. Pathogens like Cutibacterium acnes, Staphylococcus aureus, Actinomyces, etc.

Genetic Components:

There are no proven studies for the association of SAPHO with genetic factors. However, some studies show human leukocyte antigen (HLA) and genes on chromosome 18 can cause SAPHO.

Immunological Components:

An increase in the production of interleukins and tumor necrosis factor (TNF) are predisposed to SAPHO syndrome.

What Are the Clinical Features of SAPHO?

The most commonly affected regions of bone and joints are the anterior chest wall (90 % of the patients), lower extremity areas like knee and ankle joint, and hip joint. The next commonly affected sites include the spine and rarely the lower jaw.

• Pain, tenderness, swelling in the bones and joints (arthritis).

• The soft tissue surrounding the bone looks red and swollen.

• Narrowing of the joint space and destruction of bone are also found.

• Excessive bone growth and fusion of joints.

The Characteristic Features of the Skin Include:

• Nodulocystic acne is a bump on the skin formed due to excessive oil and dead cells that get clogged within the skin pores, mainly involving the face, chest, and back. It gets resolved, leaving a scar behind, common in males.

• Palmoplantar pustulosis (PPP) are painful blisters on the skin filled with yellow-colored pus. It primarily affects the palms and soles and is more common among females.

• Plaque psoriasis is yet another feature found in patients with SAPHO syndrome. It is a raised red lesion on the skin, covered by silvery scales.

• These skin lesions can occur before bone and joint manifestations, or they both can co-occur. Generally, an interval of two years is found between skin lesions and bone manifestations.

• The other systemic findings include fatigue, fever, and inflammatory bowel disease (IBD) in specific individuals. IBD causes pain and swelling along the entire portion or parts of the intestine.

What Are the Radiologic Findings of SAPHO?

• Bone scans like scintigraphy help to rule out other malignant conditions. Scintigraphy of the anterior chest wall shows a typical “bull’s head” image. It was investigated first by Freyschmidt and Sternberg.

• Radiographs can show any disorders of the tendon or ligament, bone destruction, or bone growth and expansion of the bone. Vertebral body corner lesions are spinal tissue injuries that lead to inflammation of the endplates of the spine and are also detected in radiographs.

• Magnetic resonance imaging (MRI) helps detect stiffness of joints (ankylosis), inflammation of bone marrow (osteitis) of the chest bone, lower jaw, etc. It also helps visualize surrounding soft tissue, which is not detected in plain radiographs. In addition, bony changes like an increase in the thickness of the outer surface of the bone (cortex) and narrowing of the inner portion of the bone (medulla) that occurs in hyperostosis can be detected using MRI.

What Are the Laboratory Findings of SAPHO?

In patients with SAPHO syndrome, the laboratory findings may show a mild increase in the C-reactive protein (CRP) levels and erythrocyte sedimentation rate (ESR) levels. In addition, a slight increase in white blood cells and platelets is found in some patients. Mild anemia is noted in a few others.

How Is SAPHO Diagnosed?

It is challenging to diagnose SAPHO syndrome, as all the characteristic skin and bone lesions do not coincide. However, specific examinations help in proper diagnosis.

Physical Examination:

A clinical examination of the patient and a detailed medical history are essential. In addition, inquiring the patient about back pain, joint pain, tenderness, or stiffness also helps determine any spine lesions.

Radiological Examination:

Plain radiographs and magnetic resonance imaging of the whole body or particular region (hip joint, knee) can help rule out other bone disorders.

Histological Examination:

Bone biopsy and culture are done to identify the presence of bacteria causing skin and bone lesions in SAPHO syndrome. It also helps in differentiating other non-bacterial bone lesions.

What Are the Differential Diagnoses of SAPHO?

It is often confused with the following disorders, as they have similar manifestations as that of SAPHO syndrome:

• Psoriatic Arthritis: Arthritis of joints, blisters on the skin, and spinal deformities are features of particular psoriatic arthritis. However, the radiographic features of both are different. Therefore, it poses a challenge in diagnosing SAPHO syndrome.

• Osteomyelitis: It also has clinical features like bone tenderness, fever, etc., but in most cases, osteomyelitis remains localized contrary to SAPHO syndrome, which affects various bones and joints.

• Malignant Tumors: Tumor involving the bone has similar clinical features as bone pain, tenderness, and swelling. A bone biopsy is done for accurate diagnosis.

How to Treat SAPHO?

• Pain Killers: The common non-steroidal anti-inflammatory drugs (NSAIDs) used in the treatment are Naproxen 500 mg and Ibuprofen 600 to 800 mg.

• Antibiotics: The primarily used antibiotics are Doxycycline (Tetracycline), Azithromycin, Sulfamethoxazole, etc. It helps in the management of acne and also bone lesions that are caused by bacteria. But it has side effects like nausea, vomiting, loss of appetite, etc.

• TNF Inhibitors: Tumor necrosis factor (TNF) inhibitor drugs like Etanercept and Adalimumab can be used in patients who show inadequate response to NSAIDs. It also helps in improving the symptoms of SAPHO.

• Retinoids: Dermatologists use retinoid drugs like Isotretinoin and topical corticosteroids to treat severe acne in patients with SAPHO syndrome.

• Other medications used in the treatment are Calcitonin, Colchicine, etc.

• Physiotherapy is also advised in patients with bone disorders.

• Surgery remains the last option to relieve pain in patients with severe bone destruction or if there is a loss of function.

Conclusion:

SAPHO syndrome is a rare condition that does not progress in a few patients but may cause problems in some. A detailed examination, including radiographs, can help differentiate other bone and joint disorders. This aids in providing appropriate treatment.