A 46-Year-Old Man With Spine Pain and a Rash

Herbert S. Diamond, MD, MACP


February 26, 2020


The patient described the gradual onset of an inflammatory polyarthritis. The condition involved peripheral joints, including a DIP joint; tendon sheaths, as exemplified by the swelling in the forearm; and the lumbar and cervical spine. Physical examination confirmed a pauciarticular, asymmetrical arthritis, and the presence of inflammation was indicated by the erythema and warmth of the involved joints. Although the laboratory studies were unrevealing, the patient’s radiograph showed erosive arthritis of a DIP joint, and the absence of juxta-articular osteoporosis was noted. All of these findings, which also included a rash on the scalp and intragluteal cleft, were consistent with psoriatic arthritis. The patient was started on naproxen 500 mg twice daily and oral methotrexate 15 mg once weekly, with monitoring of blood counts and liver function.

Psoriatic arthritis occurs in up to 1% of the adult white population but is less frequent in other racial groups. Onset can occur at any age, including childhood and old age. The sex ratio is equal. The incidence of psoriatic arthritis in patients with psoriasis may be as high as 30%, although some studies have reported a lower incidence. Psoriasis typically precedes the onset of arthritis, usually by no more than 10 years. However, in some patients, the onset is simultaneous, and in a minority of cases, arthritis is the first symptom.[1,2,3]

Psoriatic arthritis is associated with a strong genetic predisposition; a family history of psoriasis, arthritis, or both is often present. Multiple genes that predispose to either psoriasis or psoriatic arthritis have been identified, including human leukocyte antigen (HLA)-associated genes and non-HLA genes. Still, most of the genetic predisposition remains to be determined. Although genes that predispose to psoriasis and those that predispose to psoriatic arthritis overlap, important differences among the predisposing genes are observed.

The rash in psoriatic arthritis is erythematous and scaling. It most often occurs in plaques but may develop in a guttate pattern or, rarely, as a diffuse erythema. An example is shown in the image below.

Figure 1.

The scalp is frequently involved, although scalp psoriasis is often misdiagnosed as seborrhea. When the rash involves skin folds, scaling may be absent. An example is shown in the image below.

Figure 2.

Nail involvement is frequent and can include dystrophic changes, cracking, pitting, and splinter hemorrhages.

Early in the disease, joint involvement is most often in the form of an asymmetrical arthritis. The DIP joints are frequently involved, and cervical and lumbar spine involvement develops in 50% of patients. Tendon sheaths are often affected as well, which may result in diffuse swelling of the digits (so-called sausage digits). Diffuse, edematous swelling of a distal extremity may also occur, due to extensive tendon sheath inflammation. As in ankylosing spondylitis, involvement of tendon and ligament insertions (entheseal involvement) is common.

A minority of patients with psoriatic arthritis present with a diffuse, symmetrical pattern of arthritis or with isolated spinal involvement. In rare cases, patients have a pattern of severe, highly destructive bone resorption that, when it occurs, often affects the small joints of the hands and feet; this pattern is often refractory to treatment.[1,3]


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